This one-of-a-kind Halloween dessert is a real show-stopper with the beautiful web detail on top of the trifle.
Prepare Sponge Cake.
3-oz. (90 g) package (12 unfilled ladyfingers, split) can also be substituted for sponge cake. Arrange ladyfingers in two layers, cutting as needed to fit bowl.
Sprinkle gelatin over cold water in small bowl; let stand 1 minute to soften. Add boiling water; stir until gelatin is completely dissolved (mixture must be clear).
Stir together sugar and cocoa in large cold bowl; add whipping cream and vanilla. Beat on medium speed of electric mixer until stiff. Pour in gelatin mixture; stir until well blended.
To assemble trifle: Cut or tear cake into uneven 1 to 1-1/2-inch (2.5 to 4 cm) pieces. Layer about half of the pieces in bottom of 2-quart (2 L) straight-sided soufflé dish or trifle bowl. Sprinkle surface of cake with 2 tbsps (30 mL) chocolate chips. Spoon 2 cups (500 mL) chocolate mousse evenly over cake and chips. Remove wrappers from peanut butter cups; position cups on opposite sides of bowl so that the top of peanut butter cup (larger circle) is against side of bowl. This will be "nose" of hidden spiders. Position two closely shaped cake pieces on either side of each peanut butter cup to form white section of eyes. Position bottom of chocolate chip against glass and in center of each cake section to form pupil of eye. Fill in space between sets of eyes with mousse. Layer with remaining cake pieces, remaining chocolate chips and remaining mousse. Loosely cover; refrigerate at least 2 hours.
Just before serving, cover mousse with sweetened whipped cream or whipped topping. Spread evenly so that you have an almost flat surface. Swirl syrup in spiral pattern over top of whipped cream. Drag toothpick from center of spiral to edge of bowl. Repeat until top of trifle resembles spider web. Cover; refrigerate leftovers.
Sponge Cake: Heat oven to 350°F (180°C). Grease and flour one 8-inch (20x5 cm) round baking pan. Beat eggs in medium bowl on high speed of electric mixer until foamy. Gradually add sugar, beating until mixture is double in volume. Combine flour, baking powder and salt; add alternately with water and vanilla to egg mixture, beating on low speed just until ingredients are combined. Immediately pour batter into prepared pan. Bake 22 to 25 minutes or until cake springs back when touched lightly. Cool 5 minutes; remove from pan to wire rack. Cool completely.