01 -
Preheat oven to 325°F. Line a 9x13-inch baking pan with non-stick foil or parchment paper and spray with baking spray.
02 -
In a large mixing bowl, combine cake mix, melted butter, one egg and 2/3 cup milk. Stir until well mixed - the batter will be thick, similar to brownie batter. Divide the batter equally among 6 small bowls.
03 -
Add food coloring to each bowl to create purple, blue, green, yellow, orange, and pink batters. Take out 1 tablespoon of each colored batter and set aside for the topping.
04 -
Drop teaspoonfuls of the different colored batters randomly into the bottom of the prepared pan, alternating colors as you go. Once all the batter is used, slightly wet your hands and gently press to flatten the batter evenly across the pan.
05 -
Add 1 1/2 teaspoons milk to each of the reserved tablespoons of colored batter to thin them out for swirling.
06 -
In a bowl, beat cream cheese and sugar until smooth and creamy. Add egg and vanilla extract, mixing until well combined. Pour this cheesecake filling evenly over the rainbow cake batter layer.
07 -
Drizzle the thinned colored batters over the cheesecake layer. Use a knife or fork to gently swirl the colors together, creating a marbled effect.
08 -
Bake uncovered for 20 minutes, then cover the pan with aluminum foil to prevent the colors from browning. Continue baking for another 14-20 minutes. The center will still jiggle slightly but will firm up as it cools.
09 -
Allow the bars to cool at room temperature for about an hour, then refrigerate for at least 2 hours before cutting into 24 squares. Store any leftovers in the refrigerator.