12 Tablespoons Unsalted Danish Creamery Butter, room temperature, plus more for pan
2 ¾ cups all-purpose flour
2 teaspoons baking powder
½ teaspoon baking soda
1 ½ cups granulated white sugar
¾ teaspoon fine salt
2 large eggs plus 2 egg whites, room temperature
½ cup sour cream, room temperature
1 Tablespoon vanilla extract
1 cup whole milk, room temperature
¾ cup sweetened shredded coconut, divided
white chocolate curls, for decorating
White Chocolate Buttercream
12 ounces white chocolate, chopped into 1/2-inch pieces
1 ½ cups Unsalted Danish Creamery Butter, room temperature
¼ teaspoon fine salt
2 ½ cups powdered sugar, plus more if needed
Preheat oven to 350° F. Butter three 6-inch round cake pans and line them with parchment paper rounds; butter parchment.
In a medium bowl, whisk together flour, baking powder, and baking soda.
Place butter, sugar, and salt in the bowl of a stand mixer fitted with a paddle attachment. Cream on medium-low speed until light and fluffy, about 5 minutes, scraping down bowl as needed.
Mix in the eggs and egg whites, one at a time, until just combined, scraping bowl once or twice. Beat in sour cream and vanilla (mixture will look curdled, that’s okay). Add the dry ingredients and slowly mix until just combined. With the mixer running, slowly add milk and mix until combined and smooth.
Divide batter across prepared pans, about 15.5 ounces each for perfectly even layers. Use an offset spatula to spread surface smooth. Bake until tops are springy and golden brown and a toothpick inserted into the center comes out clean, about 40 minutes. Let cool 10 minutes in pans, then run a knife around the edges and turn out onto a rack. Peel off parchment and cool completely.
Mix 1 ½ cups white chocolate buttercream with ¼ cup shredded coconut. If needed, use a serrated knife to even out cake layers. Place one layer on a cake stand and use an offset spatula to spread with half the buttercream mixture. Top with second layer and spread with remaining coconut buttercream mix. Place third cake on top and spread entire surface with a crumb coat of frosting. Chill 20 minutes.
Frost top and sides of cake with remaining white chocolate buttercream. Decorate with remaining ½ cup shredded coconut and white chocolate curls.
White Chocolate Buttercream
Place white chocolate in a microwave-safe bowl and heat for 30 second intervals at half power, stirring in between, until just melted. Let sit until completely cool to the touch, stirring occasionally, at least 15 minutes.
Cut butter into cubes and place in the bowl of a stand mixer fitted with a paddle attachment. Add salt and mix until just softened and smooth.
With the mixer running, slowly add melted and cooled white chocolate. Scrape down bowl, then beat again until combined.
Add powdered sugar and mix on low until just combined. Increase speed to high and beat until fluffy and smooth, about 30 seconds. Use right away.