This angel cake is flavored with cocoa powder and generously frosted with sweetened whipped cream.
In an extra-large mixing bowl, let egg whites stand at room temperature for 30 minutes. Sift the 1-1/2 cups powdered sugar, the flour, and cocoa powder together 3 times; set aside.
Add the cream of tartar and vanilla to the egg whites. Beat with an electric mixer on medium speed until soft peaks form (tips curl). Gradually add the granulated sugar, about 2 tablespoons at a time, beating until stiff peaks form.
Sift about one-fourth of the flour mixture over the beaten egg whites; fold in gently. (If bowl is too full, transfer to a larger bowl.) Repeat, folding in remaining flour mixture by fourths. Pour into an ungreased 10-inch tube pan. Using a knife, gently cut through cake batter to remove any air pockets.
Bake the cake on the lowest rack in a 350 degree F oven for 40 to 45 minutes or until the top springs back when lightly touched. Immediately invert the cake (leave in pan); cool thoroughly. Loosen side of cake from pan; remove cake.
For frosting, beat the whipping cream with an electric mixer until soft peaks form (tips curl). Add the 1/4 cup powdered sugar and beat until stiff peaks form (tips stand straight).
Split the cooled cake into 2 layers. Fill and frost cake with whipped cream mixture. Top with chocolate curls and raspberries, if you like. (If you know you'll have leftovers, dollop individual servings with the whipped cream instead of frosting the whole cake.) Makes 12 servings.