01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter. Prepare the cake batter according to package instructions, combining the mix with required eggs, oil, and water. Pour batter into the prepared dish and bake for the time specified on the box (typically 25-30 minutes) until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 20 minutes.
02 - Using the tines of a fork or the rounded handle of a wooden spoon, poke holes uniformly across the entire surface of the cooled cake. Press down firmly to create channels that reach nearly to the bottom of the pan, spacing them about 1 inch apart. This allows the gelatin to penetrate throughout the cake structure.
03 - In a medium heat-safe bowl, dissolve the strawberry gelatin powder completely in 1 cup of boiling water, stirring continuously for 2 minutes to ensure no granules remain. Gradually stir in 1/2 cup of cold water to temper the mixture. The liquid should be clear and uniformly colored.
04 - Carefully pour the prepared gelatin mixture slowly over the surface of the cake, working evenly across the entire pan. Allow the liquid to seep naturally into the holes you created. Gently tilt the pan if necessary to distribute the gelatin evenly, but avoid disturbing the cake structure. The surface should appear glossy and saturated.
05 - Refrigerate the cake uncovered for at least 2 hours, or until the gelatin is completely set and firm to the touch. This chilling period allows the gelatin to stabilize within the cake matrix, creating the characteristic layered texture.
06 - Remove the chilled cake from the refrigerator. Spread the thawed whipped topping evenly over the entire surface using an offset spatula or the back of a spoon, creating a smooth, white layer. Work gently to avoid mixing the topping with the gelatin layer beneath.
07 - Arrange fresh strawberry slices decoratively over the whipped topping. Add fresh mint leaves as a finishing accent if desired. Cut into 12 equal squares and serve immediately, or return to the refrigerator until ready to serve. For cleanest cuts, wipe your knife between slices.