Angel Cake with Mocha Buttercream

CAKE
1 1/2 cups powdered sugar
1 cup cake flour
1 dash salt
10 large egg whites
1 1/2 teaspoons cream of tartar
3/4 cup sugar

BUTTERCREAM:
1 1/2 cups butter
4 tablespoons instant coffee
2 tablespoons sifted cocoa
2 cups powdered sugar

All dry ingredients should be sifted. Therefore, start by sifting together powdered sugar and cake flour. Add salt. In a large dry bowl whisk egg whites until soft peaks form. Add cream of tartar at the end. Gradually add granulated sugar to egg whites, whisking all the time. Sift 1/3 of flour mixture over egg whites, lightly fold in. Repeat with remaining flour mixture, little by little. Turn batter into a large ungreased tube pan. Smooth top. Bake at 350ºF for about 40 minutes or till cake is done. Cool cake.

Loosen around edges, remove cake from pan. Make butter cream by beating butter until very soft and smooth. Add coffee, cocoa, and powdered sugar. Beat until very light. Spread mixture in between layers and around cake. Garnish with chocolate sprinkles.