Separate eggs. Allow egg whites and yolks to stand at room temperature for 30 minutes. Meanwhile, grease a 15x10x1-inch baking pan. Line with parchment paper, making sure you have at least a 1-inch over hang on two sides; grease paper. Set pan aside. In a medium bowl stir together flour and baking powder; set aside.
Preheat oven to 375 degrees F. In a medium mixing bowl beat egg yolks and 1/2 teaspoon vanilla with an electric mixer on high speed about 5 minutes or until thick and lemon color. Gradually add 1/3 cup granulated sugar, beating on high speed until sugar is almost dissolved.
Thoroughly wash beaters. In another bowl beat egg whites on medium speed until soft peaks form (tips curl). Gradually beat in the 1/2 cup granulated sugar, beating until stiff peaks form (tips stand straight). Fold egg yolk mixture into beaten egg whites. Sprinkle flour mixture over egg mixture; fold in gently just until combined. Remove 4 tablespoons of batter and divide evenly between 2 small bowls. Carefully fold the blue food coloring into one bowl and the red food coloring into the other bowl. Transfer each colored batter into a quart-size resealable plastic bag. Snip a small hole from one corner of each bag.
With a short side of the prepared pan closest to you, carefully pipe firework designs onto the parchment paper. Bake for 1 to 2 minutes or until batter surface looks dry. Carefully spread remaining uncolored cake batter evenly over fireworks.
Bake for 12 to 15 minutes or until cake springs back when lightly touched. Immediately loosen edges of cake from pan and carefully remove cake using parchment paper overhang to lift. Cool completely on a wire rack.
In a medium bowl combine whipped topping, cream cheese, powdered sugar, and 1/2 teaspoon vanilla. Fold in sprinkles, if using.
Spread frosting onto the cooled cake, leaving about a 1-inch border. Roll cake up, carefully removing the parchment. Chill at least 4 hours before serving.