For the Sponge Cake

1. Preheat oven to 375°F.
2. Line a square 8×8 inch pan with two 8×12 inch pieces of parchment crossed so each piece overhangs two sides of the cake pan.  Set aside.
3. In the bowl of an electric mixer, whisk together the eggs and sugar by hand.
4. Place the bowl over a pot of simmering water and gently whisk, for around tree minutes, until the mixture reaches 140°F on a candy thermometer. 
5. Remove the bowl from the simmering water and whip the eggs with the electric mixer, using the whisk attachment, until the mixture is pale yellow and almost triple in volume – around 5-8 minutes.
6. Sift the flour over the egg mixture in two batches, carefully folding in the flour with a large spatula.
7. Lighted the melted margarine by stirring in a dollop of the cake batter, then gently fold the mixture into the cake batter until it is completely blended.
8. Carefully pour the batter into the prepared cake pan, smoothing the top with the spatula.
9. Bake for 20 minutes until the top is browned.
10. Allow the cake to cool completely on a wire rack.
11. Once the cake is completely cooled, run a knife or metal spatula around the edges of the cake to release it from the sides of the pan.  Remove the cake from the pan by lifting it with the parchment overhang.  Place the cake on a large cutting board.
12. Reline the pan with two more parchment sheets.
13. Using a long serrated knife, slowly slice the cake into two even layers.
14. Place the top layer back into the lined pan.
15. Cut the cake into triangles, then using a small triangle cookie cutter, cut a triangular center out of each cake triangle. Set aside.

For the Filling

1. Using an offset spatula, carefully spread the softened vanilla ice cream over the cake layer in the pan.  Smooth the top.
2. Spread the fruit sorbet over the vanilla ice cream, being careful not to press too hard so as to disturb the vanilla ice cream underneath.  Using an offset spatula, smooth the top of the sorbet.

To Finish

1. Very carefully flip the cut cake onto the sorbet, parchment side up.  Slowly peel the parchment paper off of the cake, gently pressing down on the cake as necessary.
2. Cover the cake tightly with plastic wrap and freeze for at least 6 hours.
3. Remove the cake from the freezer.  Gently run a knife or metal spatula around the edges of the cake to release it from the pan.
4. Lift the cake out of the pan and place it on a large cutting board.
5. Using a very sharp 7-8 inch chopping knife, cut the cake into triangles.  Sprinkle the pieces with powdered sugar and top with fruit jelly filling.
6. Serve garnished with additional fruit.