Step 1: Bake the Cake
Preheat your oven according to the cake mix package directions (usually 350°F). Grease a 9×13-inch baking pan with cooking spray or butter. Prepare the cake batter according to package directions, mixing until smooth and well combined. Pour the batter into the prepared pan and spread evenly. Bake according to package timing (typically 28-32 minutes) until a toothpick inserted in the center comes out clean. The top should be golden and spring back when lightly touched.

Step 2: Poke the Holes
As soon as the cake comes out of the oven, let it cool in the pan for about 15 minutes—it should still be quite warm. Using the handle of a wooden spoon, a chopstick, or a similar tool about ½-inch in diameter, poke holes all over the cake, spacing them about 1 inch apart. Make the holes go almost to the bottom of the cake but not quite through. You should have approximately 50-70 holes covering the entire surface. Don’t be shy about this step—the more holes, the more Jello flavor infuses the cake!

Step 3: Prepare the Jello
While the cake is cooling slightly, prepare your Jello mixtures. In separate bowls, empty each box of Jello gelatin. Add 1 cup of boiling water to each bowl and whisk vigorously for 2 minutes until the gelatin is completely dissolved. Then add 1 cup of cold water to each bowl and stir well. Let the Jello mixtures cool for about 5 minutes—you want them liquid but not hot enough to melt the cake.

Step 4: Pour the Jello
Working with one color at a time, slowly pour the Jello mixture over the cake, concentrating on filling the holes. Use a spoon to guide the liquid into the holes if needed. Start with one corner and work your way across in sections with each color, creating a pattern or pouring randomly for a marbled effect. The cake will absorb some Jello, and some will pool on top—this is perfect! The excess Jello will set on the surface, creating a beautiful glossy finish.

Step 5: Refrigerate
Cover the cake pan tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight. This allows the Jello to fully set within the cake and develop the best flavor and texture. The longer it chills, the better the flavors meld together.

Step 6: Make the Whipped Cream
About 30 minutes before serving, make your whipped cream topping. In a large, cold mixing bowl, combine the heavy whipping cream, powdered sugar, and vanilla extract. Using an electric mixer, beat on medium-low speed for 30 seconds, then increase to medium-high and beat for 2-3 minutes until stiff peaks form. The cream should be thick, fluffy, and hold its shape. Be careful not to overbeat or it will become grainy.

Step 7: Assemble and Serve
Spread the whipped cream evenly over the top of the chilled cake using an offset spatula or the back of a spoon. You can spread it smooth for a clean look or create decorative swirls for texture. If desired, garnish with fresh berries and mint leaves. Slice into squares and serve immediately. Each slice will reveal beautiful streaks of colorful Jello throughout!