Preheat oven to 350 and line a 10x15x1 baking sheet with parchment paper. Spray the parchment paper with nonstick cooking spray. Set aside.

Line 1 muffin tin with 5 paper liners and set aside.

Add eggs to a mixer and beat on high for 5-6 minutes until bubbly and frothy. Add cake, sour cream, water and oil. Beat for 30 seconds on low and scrape down the sides of the bowl. Beat on medium for 1 minute until combined well.

Pour 3-½ cups of batter into a separate bowl. Use a 3 tablespoon portion scoop to scoop remaining batter into 5 cupcake liners. Bake cupcakes according to package directions.

With remaining 3-½ cups batter, divide into 4 equal bowls and color each bowl a separate color with food coloring. Place each color of batter into a separate pastry bag and snip the tips.

Pipe the batter onto the prepared pan in a diagonal pattern, alternating colors. Gently tap the pan to fill in any gaps and evenly spread the batter.

Bake for 8-12 minutes or until cake is done in the center when a toothpick is inserted in it. Remove from oven.

For the cake roll, generously sprinkle powdered sugar onto a thin, clean towel. Let the cake cool for 10 minutes before removing it from the pan and placing it onto the powder sugar covered towel. Place the cake roll top down on the towel, so the bottom/darker part of the cake faces up. Discard the parchment paper. Starting on a short end, roll the towel and cake into log shape. Set aside to cool completely.

To make the icing, mix together the frosting and whipped topping.

Carefully unroll cooled cake roll and spread icing on the top. Sprinkle with sprinkles. Roll back up and wrap with plastic wrap. Refrigerate for 2 hours or until ready to serve. When ready to serve, unwrap and slice into 12 slices, about 1" wide.

Store any leftover cake roll covered and in the refrigerator.