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1
Preheat oven to 350 degrees F (175 degrees C). Grease and flour three 9-inch baking pans.
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2
Mix flour, baking powder, and salt together in a bowl.
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3
Place white chocolate in a microwave-safe bowl; cook in microwave on high until melted, stirring between 30 second intervals, until smooth.
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4
Beat 1 1/4 cup butter and 2 1/4 cups sugar together in a large bowl until light and fluffy. Beat in 5 egg yolks, one at a time, until incorporated. Stir in melted white chocolate and 1 teaspoon vanilla extract until evenly mixed. Beat flour mixture into butter-white chocolate mixture, alternating with buttermilk, until just mixed.
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5
Beat the 5 egg whites in a separate bowl until stiff peaks form. Lift your beater or whisk straight up: the egg whites should form a sharp peak that holds its shape. Fold egg whites into the cake batter. Divide batter among the three prepared baking pans.
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6
Bake in the preheated oven until a toothpick inserted in the center of each cake comes out clean, 35 to 40 minutes. Cool cakes in pans for 10 minutes before transferring to wire rack to cool completely.
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7
Whisk 4 egg yolks, evaporated milk, and 1 1/2 teaspoons vanilla extract in a large saucepan until well blended. Add 1 1/2 cup white sugar and 3/4 cup butter; cook over medium heat until thickened and golden brown, stirring constantly, about 12 minutes. Remove from heat. Stir coconut and pecans into frosting mixture. Cool to room temperature.
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8
Place one cake on a serving plate. Spread a layer of coconut frosting on top of cake. Place second cake on top of frosting layer; spread with a layer of coconut frosting. Place last cake on top; frost top and sides of cake with remaining frosting.
