Mint and lime infused light and fluffy white cake layers with lime curd and mint buttercream.
On a microwave safe plate, layer two paper towels. Place the mint leaves in a single layer on the paper towels and cover with another paper towel. Microwave the mint leaves on medium-high heat in 30 second intervals, until the leaves are crispy but not burnt or brown.
An alternative to dehydrating the leaves in the microwave is using an air fryer or buying dried mint leaves. If you use dried mint leaves, you'll want to use a tablespoon.
Once the leaves are dehydrated, place the leaves, zest of the two limes and the sugar in a food processor. Blend until the mint leaves and zest are well blended in the sugar.
Using a fine mesh strainer, push the sugar mixture through the strainer to get rid of any large chunks of mint and lime. You'll use this sugar in the cake recipe instructions below.
Preheat your oven to 325 degrees F. Spray three 8-inch round cake pans with non-stick spray, line the bottom with parchment paper and spray again. Set aside.
In a medium sized mixing bowl, combine the flour, baking powder and salt. Whisk to combine. Set aside.
In a stand mixer fitted with the paddle attachment, combine the granulated sugar, the mint lime sugar and the butter. Beat on medium-high speed for 2 to 3 minutes, scraping down the sides and the bottom of the bowl half way through. You want the sugar and butter mixture to get light in color and texture.
Add the sour cream and mix until well blended.
With the mixer on low speed, alternately add the dry ingredients and the buttermilk, starting and ending with the dry ingredients. The mixture will be thick.
In a stainless steel bowl, whisk the egg whites until stiff peaks form.
Fold the egg whites into the cake batter.
Evenly distribute the cake batter into the prepared pans, about 16 ounces in each of the 8-inch pans. (You can also do four 6-inch pans with about 12 ounces of batter in each pan).
Bake the cake layers for about 23 to 25 minutes, or until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it.
Allow the cake to cool in the pans on a wire rack for about 10 to 15 minutes before inverting the layers onto the racks to cool completely. To ensure your layers don't stick to your cooling racks, spray the racks with nonstick spray. Allow the cakes to cool completely before using or wrapping plastic wrap to store in the freezer for another day.
In a small sauce pan, combine the sugar, lime juice, and lime zest over medium heat. Stir until the sugar is dissolved. Add the egg yolks and whole eggs, stirring while you add them. Continue to stir while the mixture cooks for about 5 to 6 minutes. The mixture will thicken during this time. Remove it from the heat and add the butter. Stir until smooth.
Run the curd through a fine mesh sieve. Once cooled, place plastic wrap directly on top of the curd and refrigerate for at least 4 hours.
To make the mint cream, combine the cream and mint leaves over low heat and simmer for 10 to 15 minutes. Turn off the heat and let steep for another 15 minutes. Cool completely before using in the buttercream.
In a stand mixer fitted with a paddle attachment, beat the butter on medium-high speed for 2 to 3 minutes, until light and fluffy.
With the mixer on low speed, gradually add the sifted powdered sugar, followed by the flavored cream.
Turn the mixer to medium speed and beat the frosting until it is light and fluffy, about 2 to 3 minutes. Before frosting your cake, make sure to mix the frosting by hand with a wooden spoon to push out the air pockets.
Level each cake layer with a knife or cake leveler, if needed.
Place your first cake layer, top-side up, on a cake plate or cake board. Cover the cake layer with 1/2 cup buttercream and then pipe a rim of the buttercream around the cake to act as a barrier to the lime curd.
Pour and spread about 1/4 cup over the cake layer.
Repeat these steps for the second layer of cake.
Place the final cake layer, top-side down, on the second layer of buttercream and curd. Frost the entire cake with a thin coat of frosting to lock in the crumbs. Freeze the crumb coat for 10 to 15 minutes.
After the crumb coat is chilled, continue frosting the cake and decorate with leftover buttercream and limes.