Prepare Simply Delicious Citrus Sponge Cake in an 8x8x2-inch baking pan; set aside. (Do not prepare filling for cake.)
Meanwhile, for custard sauce, in a heavy medium saucepan combine sugar and flour. Stir in milk and egg product. Cook and stir over medium heat until mixture is thickened and bubbly. Cook and stir 1 minute more. Remove from heat. Stir in margarine, orange peel, and 1/2 cup orange juice. Cool thoroughly.
To assemble trifle, cut cake into 1-1/2-inch cubes. In a 2-quart glass bowl arrange half of cake cubes. Sprinkle cake with 1 tablespoon of the sherry or orange juice. Top with half of the peaches, strawberries, and blueberries. Pour half of custard over fruit. Repeat layers. Pipe or spread dessert topping on top. Cover and chill 2 to 8 hours or until serving time. If desired, garnish with additional strawberries, blueberries, and mint. Makes 10 servings.