Coconut Macadamia Rum Cake (Gluten Free! Grain Free!)

Inspired by the coconut rum I picked up in Honolulu, this delicious cake combines many flavors of the Hawaiian islands. It’s like a luau in your mouth!

Coconut Macadamia Rum Cake with Grilled Pineapple Filling (Gluten Free!)

Ingredients

Grilled Pineapple Curd

  • 2 c chopped fresh pineapple about 1 small – medium pineapple
  • 1 Tbsp coconut oil see notes
  • 1 Tbsp pineapple juice if needed for pureeing
  • 1/4 c sugar
  • 3 egg yolks
  • 2 Tbsp corn starch
  • 1 pinch salt
  • 2 Tbsp butter

Coconut Rum Cake

  • 1 c coconut flour
  • 1 c all purpose gluten free flour or traditional AP flour see notes
  • 1.5 c sugar
  • 3.7 oz box instant vanilla pudding
  • 2 tsp baking powder
  • 1 tsp salt
  • 1/2 c unsalted butter room temperature
  • 1/2 c vegetable oil
  • 1/2 c milk room temperature
  • 4 large eggs room temperature
  • 1/2 c coconut rum
  • 2 tsp vanilla or coconut extract
  • 1.5 tsp xanthan gum optional, see notes
  • 1 c macadamia nuts roughly chopped

Rum Syrup

  • 8 Tbsp unsalted butter
  • 1/4 c water
  • 1 c sugar
  • 1 pinch salt
  • 1/2 c coconut rum
  • 1/2 tsp vanilla extract

Instructions

Grilled Pineapple Curd

  • Chop one small to medium pineapple into wedges.
  • Preheat and lightly oil outdoor grill or indoor grill pan, and cook pineapple pieces to desired level of char: about 3-8 minutes per side. Remove pieces to high powered blender or food processor.
  • Puree the pieces in a high speed blender. Strain through a fine mesh.
  • Place pineapple puree, sugar, egg yolks, corn starch, and salt to a small sauce pan. Bring to a low and slow simmer on medium heat, whisking continuously until thickened: the curd should coat the back of a wooden spoon without dripping.
  • Remove from heat, whisk in the butter, and set aside to cool.
  • Grilled pineapple curd can be made ahead of time. In an airtight container, it’s good for 2-3 days in the refrigerator and up to 6 months in the freezer.

Coconut Macadamia Rum Cake with Grilled Pineapple Filling

  • Preheat oven to 325°F.
  • Place all dry ingredients in a medium mixing bowl, and briefly whisk to combine.
  • Add butter and vegetable oil to the bowl and mix on medium speed until it’s crumbly and sandy.
  • Beat in the milk, then beat in the eggs one at a time. Scrape down the side of the bowl and mix until again until well-combined.
  • Mix in the coconut rum and vanilla extract.
  • Divide the batter roughly in half, and add the chopped macadamia nuts to one half.
  • Prepare a standard 10 cup bundt pan with homemade pan release
  • Fill the pan with the half of the batter that contains chopped macadamia nuts.
  • With the back of a spoon, press a small moat into the batter in the pan, all the way around, and fill it with grilled pineapple curd.
  • Add the remaining batter to the bundt pan, and bake 50-60 minutes.

Coconut Rum Sauce

  • Make the rum sauce while the cake is cooling. Combine all of the ingredients except the vanilla to a small saucepan. Bring to a boil, then reduce and simmer 6-10 minutes to thicken into a syrup. 
  • Remove from heat and stir in the vanilla extract.
  • Using a long skewer, poke holes throughout the cake. Pour the syrup over the cake and into the holes a bit at a time until it’s all incorporated. 
  • Cover and let sit overnight.
  • Uncover, place a plate upside down over the bundt pan, and carefully invert. 
  • Enjoy!

Notes

You may use traditional all-purpose flour, or any gluten free all purpose flour blend. If using traditional ap flour, or if your gluten free ap flour blend contains xanthan gum, omit it from the recipe. If your gf flour blend does not contain xanthan gum, add 1.5 tsp to your flour prior to blending with the other ingredients.
Read on below for more gluten free flour tips!

From Momcation to Inspiration

This cake began with an impulse buy. I was momcationing in Honolulu, and popped into one of those ubiquitous ABC Stores. The ABC Stores are absolutely over priced on some items, but absolutely convenient: They have EVERYTHING and they are EVERYWHERE. I was on the hunt for a particular nut butter that I had purchased there on a previous trip: macadamia nut honey coconut peanut butter. It sounds like a mouthful, and that’s fitting because I just want to eat it by the spoonful. It’s so perfect on top of my favorite buckwheat waffles that I almost don’t want to make them without this nut butter.

I scoured every ABC Store in Waikiki and didn’t find it, but the sampler pack of Koloa rums did catch my eye. On tasting them with my husband after returning home, we were particularly taken with their coconut rum. It’s amazing in a cocktail, but this rum begged for something a little more special. Remembering the rum cakes that my aunt made years ago, that us kids were never allowed to taste, I wondered how a coconut version might fare. Perfectly, it turns out!

The Perfect Pineapple Filling

Grilled Pineapple Curd

We begin by making a grilled pineapple curd for the cake’s filling. You can make the rum cake without it, but you’d be missing out. The mellowed pineapple layer of flavor really takes this cake to the next level! 

Xanthan Gum, Gluten, and Flours

Next up to bat is the batter, and we start with flour. You may use traditional all purpose flour, or any gluten free all purpose flour. I’ve made it several times now using a variety of ready-made gf flour blends. They’ve all turned out really well, but my favorite for texture and flavor is Cup 4 Cup’s Multipurpose Flour. It’s so good that your celiac friends just might corner you to verify that it is truly gluten free!

Whatever gf flour you use, when baking you need to look at one thing in particular: xanthan gum. Xanthan gum is essentially a gluten substitute. Some all purpose gluten free flours already contain it, and some don’t. If your gf flour does not, you’ll need to add it or one of the other gluten stand-ins!

Gluten is the “glue” that holds everything together in baking. When gasses bubble up as our baked goods cook, gluten provides the structure and elasticity to allow dough and batter to stretch and rise and contain those gasses. Without it, our breads and cakes become a flat, crumbly mess. We need to replace that gluten with something else in gluten free baking. Xanthan gum is the most common gluten substitute because it most closely approximates the results we get with gluten, but there are other options: guar gum, psyllium fiber, agar agar, and more. We’ll explore this more in a future post, but for now, the general rule is to add around 1/2 tsp xanthan gum per cup of gf flour for cookies and cakes, and 1 tsp per cup of flour for breads

Coconut Flour

This cake was made only with coconut flour!

The next addition to your mixing bowl is 1 cup of coconut flour. It has a delightful flavor, and definitely adds a pleasant texture and chew to baked goods. Being high in fiber and protein, we can almost pretend for a hot minute that this cake does something good for us, too! For a grain-free alternative, you can absolutely skip the all purpose flour altogether and make this with 2 cups of coconut flour. It comes out a bit more dense, a lot more filling, and extremely satisfying. Usually, you would need to add more liquid ingredients when baking with coconut flour as it is surprisingly absorbent, but that isn’t a problem with this extremely moist cake! Make it as-is or add more of the rum syrup at the end to achieve that glistening, saturated goodness typical of rum cakes, whichever you prefer!

Butter Snob For Life

This butter is so good, it’s almost cheese! It recently became a fab Lemon Pound Cake. So delish.

With your flours, sugar, pudding mix, baking powder, and salt in the mixing bowl, it’s time to add your room temperature butter and vegetable oil. I have a confession to make here. I’m a butter snob, and unapologetically so. Given the access and the funds, I will splurge on cultured European butter for baking every time – especially in a cake as rich as this one. Cultured butter has been treated with bacterial cultures, much like yogurt, and this adds flavor. European butter has a higher butterfat content than most American butters, and makes for richer dishes. I challenge anyone who thinks this is silly to bake two batches of your favorite cookies: one with a standard butter, and one with the best stuff you can find (which may be in the artisan cheese section of your grocery store). Gather your friends and family for a taste test, and I promise you’ll all be infected with buttersnobitis, too! Once afflicted, Kerrygold and Lurpak are both outstanding, and easy enough on the wallet for every-day meals. When you want to bang on the big drum, try Échiré, the butter with a cult following.

Mix on medium speed until you have a sandy consistency, then add your room temperature milk, still mixing. Add your room temperature eggs one at a time. Pause the mixer, scrape down the sides of the bowl, and mix again until well combined. 

Room Temp For Better Baking

Let’s pause our discussion here too, and talk about why we want room temperature ingredients when baking. Simply put, cold ingredients won’t incorporate as evenly as they would at room temp, leading to clumpy batters, less air trapped inside, and a less fluffy cake. If you’re deep into your recipe and realize that you forgot to take something out of the fridge ahead of time, we have some easy fixes. 

  • Put some water on to boil. Cut your butter into small pats and place on a plate. Pour the boiling water into a bowl, drain, and invert the hot bowl over the butter for about 5 minutes.
  • Place eggs in a bowl of warm water for 10-15 minutes. Not too hot, though! Remember that you just want it a little warmer than fridge temp, not cooked!
  • Microwave milk a few seconds at a time to take the chill off, or place a tall glass of milk inside a bowl of hot water for a few minutes.

Now it’s time to add your coconut rum and vanilla or coconut extract, and you have some choices to make. I’ve made this cake with Malibu Rum and Koloa Coconut Rum. Malibu made it sweeter, and Koloa had a more crisp and fresh coconut flavor. The Koloa was definitely also more potent, with 40% alcohol by volume compared to Malibu’s 21%. Both versions were fantastic! There are many other coconut rums out there on the market, and we’d love to hear what you used and how it turned out! Drop us a line or feel free to leave a comment below!

Coconut or Vanilla?

I prefer using vanilla extract here when I’m going for a smoother, richer overall cake, or coconut extract when I really want to highlight that flavor. The choice is yours, and you can’t go wrong either way!

Take a minute to paint some perfect pan release into every nook and cranny of your favorite bundt pan. This stuff is the bomb! It’s a baker’s secret weapon and virtually guarantees a perfect bundt cake every time.

Chopped macadamia nuts.

Now divide your batter, and add the chopped macadamia nuts to one half. Place the nutty half of the batter in the bottom of the bundt pan, and spoon the grilled pineapple curd into the middle of the batter, all the way around the pan. Pour the rest of the batter into the bundt pan, atop the filling, and bake in the oven for 50-60 minutes.

Buttered Coconut Rum Syrup!

Rum-soaked deliciousness!

When finished and while cooling, make the rum syrup. Combine the butter, water, sugar, salt, and rum to a small sauce pan, and bring to a boil. Reduce the heat and simmer 5-10 minutes to thicken, adding the vanilla extract at the end. Using a skewer, poke holes down through your cake, all the way around. Pour the rum sauce a bit at a time all over the cake, using it all. Cover and let sit overnight.

The Moment of Truth

Now for the moment of truth: getting this sticky cake out of the pan in one beautiful piece. Start by filling your sink or large basin with an inch or three of very hot water. Sit your bundt pan in the hot water for a couple of minutes to loosen up the sticky rum sauce. Remove from the sink, place an upside-down cake stand or plate over the opening of the bundt pan, and carefully invert. If you’ve used the homemade pan release, it should loosen quickly and easily. I’ve made dozens of bundt cakes using the pan release, and it’s been perfect every time! If it doesn’t let go, let it sit for a bit or give it some light taps all around. For a stubborn cake, carefully turn it over again and repeat the hot water trick or warm for 10 minutes in a 350°F oven and try again.

It’s a Luau in Your Mouth!

Your cake is ready to serve! Turn up the tunes, kick back with some strong Kona coffee, and get your Hawaiian vibes flowing! Enjoy!

Aloha!

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