Preheat and prepare the pan. Heat your oven according to the cake mix directions. Grease a 9x13-inch baking pan. This size makes the poking and serving easy.

Mix and bake the cake. Prepare the cake batter as directed on the box. For a flavor boost, add 1 teaspoon vanilla or a pinch of lemon zest. Pour the batter into the pan and bake until a toothpick comes out clean, usually 25–30 minutes.

Cool slightly. Let the cake cool for 15–20 minutes. It should be warm but not hot. This helps it hold its shape while still absorbing the gelatin.

Poke the holes. Using the handle of a wooden spoon or a thick straw, poke holes all over the cake, about 1 inch apart. Go deep but don’t break through the bottom. Wipe the tool if it gets sticky.

Make the gelatin. In a bowl, whisk the gelatin with 1 cup boiling water until fully dissolved. Stir in 1/2 cup cold water. You want it warm and pourable, not hot.

Pour the gelatin. Slowly pour the gelatin mixture over the cake, focusing on the holes. Work evenly so each slice gets color and flavor. It will look like a lot of liquid—this is normal.

Chill and set. Cover the cake and refrigerate for at least 2 hours, or until the gelatin is set and the cake is fully cool.

Add the topping. Spread the whipped topping in an even layer. For a lighter finish, use thawed whipped topping. For a richer version, beat 1 1/4 cups cold heavy cream with 2 tablespoons powdered sugar until soft peaks form.

Finish with fruit and sprinkles. Scatter sliced strawberries or your chosen fruit over the top. Add sprinkles for a birthday-ready look. Don’t overload—you want neat slices.

Chill again, then slice. Refrigerate for 30 minutes to set the top. Slice into squares and serve chilled. Clean the knife between cuts for tidy edges.