This coconut Key lime cake is an ode to the pending summer. With sweet and tart lime-scented layers and a marshmallow frosting coated in loads of toasted coconut, it’s basically summer in a dessert. I opted to make and share the recipe now because I had a hunch you all may be looking for some alternative treats on these spring days that feel like mid-July. If you’re as ready for sunshine as I am, let’s grab our forks and chat about the ins and outs of this cake.
The layers of this coconut Key lime cake are scented in two ways. The zest of Key limes contributes that notable lime flavor while the juice of the limes adds a tart punch and acidity. The cake layers bake up moist and fluffy, slightly more dense than a white cake but with a fine crumb. The frosting here is an old-fashioned seven-minute frosting. Not familiar? Egg whites and sugar whip up into a fluffy, marshmallow-esque frosting that is ultra-white, super sticky and kinda cloud-like. The coconut flavor comes from the smidgen of coconut extract before it’s slathered on the layers of cake. To keep the cake from sticking to everything in its path (and to add a ton of extra coconut flavor), coat the whole thing in toasted coconut flakes. Divine.
So a few questions you may be asking about this coconut Key lime cake. Like, what if I can’t find Key limes? Totally reasonable. Substitute the same amount of regular lime juice and zest and the cake will still be fab. Scout’s honor. And what if you’re not into the seven-minute frosting? Also understandable. I’m not always game for the marshmallow flavor, and if that’s you, too, try out this buttercream from another favorite cake of mine. Just substitute some coconut extract for the almond extract.
If you need more intel on properly whipping egg whites for the frosting on this coconut Key lime cake, you should revisit my last “You Need to Know” post. I chat about all the ins and outs of whipping egg whites, so if you’re in the dark, start here. I hope you all get around to making this coconut Key lime cake as soon as possible. It’s sure to get you in the mood for summer.
Coconut Key Lime Cake
Prep time: 25 minutes
Cook time: 30 minutes
Total time: 55 minutes
For the cake:
- 1 cup (230 gm) unsalted butter, at room temperature
- 2 1/4 cups (450 gm) sugar
- 3 large eggs, at room temperature
- 1 cup (240 gm) buttermilk, at room temperature
- 2 tablespoons Key lime zest
- 6 tablespoons Key lime juice
- 3 cups (420 gm) all-purpose flour
- 1 teaspoon baking soda
- 1 teaspoon salt
- ½ teaspoon baking powder
For the frosting (adapted from Sarah Kieffer):
- 5 large egg whites, at room temperature
- 1 2/3 cup sugar
- 2 tablespoons corn syrup
- ¼ teaspoon salt
- ½ teaspoon vanilla extract
- ½ teaspoon coconut extract
- 3 cups toasted coconut
To prepare the cake:
- Preheat the oven to 350 degrees and grease three 8-inch pans, lining the bottom with a round of parchment paper. Set aside.
- In a large bowl or the bowl of a stand mixer, cream the butter and sugar on medium speed for three minutes. Scrape the sides of the bowl and add the eggs, one at a time, beating for an additional minute afterward. Combine the buttermilk, zest and juice, and add half of this mixture to the butter mixture. Scrape the sides of the bowl and add the flour, baking soda, salt and baking powder, stirring on low speed. Once it’s almost combined, add the remaining milk mixture. Scrape the sides of the bowl and fold any unincorporated bits into the batter. Divide the batter among the three pans and bake in the oven until a toothpick inserted comes out clean, about 15 minutes. Allow to cool completely.
To prepare the frosting:
- Bring an inch of water to a simmer in a medium-sized saucepan on the stove.
- Meanwhile, in a large, clean bowl or the clean bowl of a stand mixer, whisk together the egg whites, sugar, corn syrup and salt. Put the bowl over the pot of gently simmering water and stir with a spatula until the sugar has melted. You can test this by carefully rubbing the mixture between two fingers. It should feel smooth. Once the mixture reaches about 165 degrees (about six minutes on the stove) remove the bowl from the heat and begin whipping the mixture on medium-high speed with a hand mixer or on your stand mixer until stiff peaks have formed, about 8-10 minutes. Add the vanilla and coconut extract and stir in.
To assemble the cake:
- Cut the domes off the baked cake layers. Use a bit of frosting to adhere one layer to an 8-inch cake board or serving plate. Spoon 3/4 cup to 1 cup of frosting on top of the layer and spread it flat. Repeat this process with the remaining two cake layers and then use the remaining frosting to frost the cake. If desired, you can coat the cake with the toasted coconut flakes, or you can use a torch to carefully toast the meringue frosting. Cake is best served the day it is assembled.