Prepare the Cake: Preheat oven to 350°F (175°C). Grease and flour three 8-inch round cake pans. In a bowl, whisk together flour, baking powder, baking soda, and salt. In a separate large bowl, beat butter and sugar until light and fluffy. Add egg whites one at a time, mixing well. Stir in vanilla extract. Alternately add dry ingredients with buttermilk and whole milk, mixing until just combined. Divide batter evenly between pans and bake for 22-25 minutes or until a toothpick inserted in the center comes out clean. Let cakes cool completely.

Make the Coconut-Pecan Frosting: In a saucepan over medium heat, whisk together evaporated milk, sugar, egg yolks, and butter. Cook, stirring constantly, until thickened (about 10 minutes). Remove from heat and stir in vanilla, coconut, and pecans. Let cool completely.

Make the White Chocolate Frosting: Beat butter until creamy. Gradually add powdered sugar, mixing well. Pour in melted white chocolate, vanilla, and heavy cream. Beat until smooth and fluffy.

Assemble the Cake: Place one cake layer on a serving plate. Spread a layer of coconut-pecan frosting. Repeat with the second layer. Place the third cake layer on top and frost the entire cake with white chocolate frosting. Garnish with extra coconut and pecans if desired.

Serve: Chill for 30 minutes before slicing for the best texture. Store leftovers in an airtight container.