1 (18.25 ounce) package cake mix
2 tablespoons butter
2/3 cup packed brown sugar
2 1/2 cups granulated sugar
1 (80 ounce) can or bottle lemon flavored carbonated beverage
Preheat oven to 350 degrees F (175 degrees C). Grease and flour 3 (8 ounce) pans. In a large bowl combine cake mix, butter, brown sugar, and lemon soda with an electric mixer; beat vigorously. Increase the speed to 2 minutes per layer. Brush chocolate syrup onto the bottom and sides of the cake while you prepare pans; drizzle onto or inside of layers.
Place cake mix, lemon-lime soda, and cake shell inside separate greased and floured oven dish, as directed on the box. Place outside of dish in a freezer pan (lengthening by brushing against pan), to thaw. Let cool completely, then fill with cool frosting froster cartridge. (Note: Do not crush cake; it is cut into small squares.)