01 -
Heat your oven to 350 degrees. Spray a 9x13 inch baking dish with non-stick baking spray.
02 -
In a medium mixing bowl, combine the cake mix, water, vegetable oil, and egg whites. Use a hand mixer on medium speed to mix everything together until completely smooth with no lumps.
03 -
Split the cake batter evenly into three separate bowls. Use glass or disposable bowls since you'll be adding food coloring that might stain.
04 -
Add 3 to 4 drops of blue gel food coloring to one bowl and stir until no streaks remain. Add 5 to 7 drops of purple gel coloring to the second bowl and stir well. Add 5 to 7 drops of pink gel coloring to the third bowl and stir until completely mixed. Adjust the number of drops based on how light or dark you want each color.
05 -
Drop spoonfuls of each colored batter randomly into the prepared baking dish. Once all the batter is in the pan, use a toothpick or bamboo skewer to gently swirl the colors together, creating a marbled effect.
06 -
Bake for 25 to 28 minutes, until a toothpick inserted in the center comes out clean. Start checking at 22 minutes since ovens vary. Take it out and let it cool completely.
07 -
Once the cake is completely cool, use the round end of a wooden spoon to poke holes all over the cake, spacing them about an inch apart.
08 -
In a large bowl, whisk together the cold milk and pudding mix using a hand mixer on low speed or a whisk. Mix for about 2 to 3 minutes until the pudding starts to thicken up nicely.
09 -
Spoon the pudding into all the holes you made until they're filled. Then spread the rest of the pudding evenly over the top of the cake using a spatula.
10 -
Spoon the thawed whipped topping over the pudding layer and use a spatula to spread it smooth and even. Cover the cake and refrigerate for at least 1 hour to set everything.
11 -
Take the cake out of the fridge and sprinkle about half a cup of the unicorn sparkle sprinkles all over the top. Cut into 15 slices (3 rows by 5 rows). Keep it refrigerated until you're ready to serve. Store any leftovers covered in the fridge for up to 3 days.