Mix powdered sugar, hot milk and vanilla. Beat until smooth. Spread icing over cake. Melt chocolate and butter over double boiler. Stir till well blended. Make circles or lines on top of cake with a string or sharp knife. Make eight evenly spaced strokes toward edge of cake. To make the web, make eight additional strokes toward the center between the eight original strokes. Spread icing over cake make chocolate lines on top of cake make eight evenly spaced strokes torte edge of cake. Circles are more attractive.