1cupunsalted butter(226 grams), softened to room temperature
LIME CURD FILLING:
½cupfresh lime juice(125 ml)
Zest of 2 limes
½cupgranulated sugar(100 grams)
5large egg yolks
¼cupunsalted butter(56 grams)
Food coloring, optional (see Notes)
5large egg whites
1 ¼cupsgranulated sugar(250 grams)
2cupsunsalted butter(4 sticks, 450 grams), at room temperature
¼cupcoconut milk or cream of coconut
Zest of 2 limes
Approximately 1 cup toasted coconut, sweetened or unsweetened
TO MAKE THE CAKE:
Preheat oven to 350 degrees. Butter and flour two or three 8-inch or 9-inch cake pans and line with parchment paper. (See Notes)
In a small bowl, whisk together the egg whites, 1/2 cup of the coconut milk, and coconut flavoring.
In the bowl of a stand mixer fitted with a paddle attachment, combine the flour, sugar, baking powder, and salt. Add the butter and remaining 1 cup coconut milk and combine on low speed until moistened. Increase speed to medium and beat until light and fluffy, about 2 minutes, scraping down the sides of the bowl as needed.
Add the egg white mixture in 3 additions, scraping down the sides of the bowl and mixing just long enough to incorporate between additions.
Divide the batter among the prepared pans and bake for 35-40 minutes or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in their pans for 10 minutes, then turn them out onto cooling racks to cool completely.
Cake layers can be made in advance. Wrap in plastic wrap and store in the fridge for up to 4 days or in the freezer for several months. Defrost before assembling.
TO MAKE THE LIME CURD:
Add the lime juice, zest, and sugar to a small saucepan set over medium heat. Heat until sugar is dissolved, stirring occasionally.
Add egg yolks to a medium bowl. While whisking constantly, add the heated lime juice mixture in a small steady stream until completely combined.
Return mixture to the saucepan and cook over medium heat until thickened, 4-5 minutes, stirring constantly. Mixture should coat the back of a spoon. Stir in butter.
Pass lemon curd though a mesh strainer to remove zest and any egg bits. Chill completely.
TO MAKE THE COCONUT-LIME BUTTERCREAM:
In the bowl of the stand mixer, combine the egg whites and sugar. Place over a pot of simmering water. The bottom of the bowl should not touch the water.
Heat egg mixture, stirring frequently, until sugar is completely melted and it's hot to the touch. For best results, insert a candy thermometer and heat mixture to 160 degrees F.
Transfer bowl to the stand mixer and beat with the whisk attachment on high speed until cooled and egg whites have medium peaks, about 5 minutes.
Reduce mixer speed to medium and add butter a tablespoon at a time. Egg whites will deflate a bit and may appear soupy, but will thicken and come together once all the butter has been added. If not, chill in the fridge for 15 minutes, then whip some more.
Stir in coconut milk or cream and lime zest and beat until light and fluffy.
TO ASSEMBLE CAKE:
Add about 1 cup of butter cream to chilled lime curd and stir until smooth.
Remove any domed cake tops and/or split cake layers if desired (see my full tutorial). Place one cake layer on a cake stand or plate.
Pipe or frost a small "dam" of buttercream around edge of the cake layer (this will keep the curd from leaking out while you assemble.). Spread 1/2 or 1/3 of lime curd mixture (depending on how many layers you have) into the center. Top with another cake layer.
Repeat with remaining cake layers.
Frost entire cake with buttercream and decorated as desired. Top with toasted coconut.
Store cake in the fridge for at least 30 minutes before serving, and leftovers may be stored in the fridge for up to 4 days.
This cake can be baked in either 8 or 9-inch pans. I prefer 8-inch as it makes a taller cake, but it's up to you. You can use 2 or 3 pans, depending on the look you're going for: double layer (2 pans), triple layer (3 pans), or quadruple layer (2 pans, then slice each layer in half). I've had some comments about the batter not fitting in two 8-inch pans. My pans are 4 inches deep and can accommodate a lot of batter. If you have only 2-inch deep pans, consider using 3 pans or 9-inch pans.
Lime curd is naturally yellow in color. If you'd like it to be green, I suggest adding a tiny bit of blue gel food coloring. You can always add more, so start small. Adding green coloring will actually make it more of a neon green color.
To toast coconut: spread into a single layer on a sheet pan and bake at 350 degrees for about 3-5 minutes. Watch closely to make sure it doesn't burn. Let cool completely.