To prepare Ice Cream Layer: In a small mixing bowl, beat peanut butter while gradually adding milk. Beat until smooth. In large bowl, stir ice cream until softened; fold in peanut butter mixture. Turn into a 9-inch round cake pan and freeze. To prepare Cake Layer: Generously butter bottom of a 9-inch round cake pan with dust with flour. In a small mixing bowl cream butter; gradually add sugar and beat until light and fluffy. Beat in egg yolks. Blend in vanilla. In a small saucepan, heat chocolate and water; stir until melted and mixture becomes smooth. Add to creamed mixture. Sift together flour and baking powder; add to creamed mixture alternately with milk, beginning and ending with dry ingredients. Beat egg whites to soft peak stage, fold into batter. Turn into prepared pan. Bake in a preheated 350?F oven for 25-30 minutes. Cool in pan on wire rack for 5 minutes. Turn cake onto rack to further cool. Then chill. To assemble Cake: place Cake Layer on serving plate. Unmold Ice Cream Layer by dipping in warm water; place on top of cake layer. Sprinkle with grated chocolate. Return to freezer. In chilled bowl with chilled beaters, whip cream. Flute cream around bottom and upper edge of cake. Serve immediately. Make 12 servings.