Preheat your oven and prepare a 9x13 inch baking pan according to the cake mix box instructions. Mix and pour the cake batter into the prepared pan, then bake according to package directions until a toothpick inserted in the center comes out clean. I always use Betty Crocker Super Moist because it stays tender and moist even after absorbing the jello liquid. Once baked, let the cake cool in the pan for 15 minutes—this is important because it allows the cake to set slightly while still being warm enough to absorb the gelatin mixture.

While the cake cools, use a fork to poke holes all over the surface of the warm cake—you want to create plenty of small holes so the jello can soak in deeply and flavor every bite. In a separate bowl, dissolve the strawberry gelatin in the boiling water, stirring for about 2 minutes until completely dissolved. I use Jell-O brand because it gives the most vibrant color that really shines through the cake. Then stir in the cold water to cool the mixture slightly—this prevents the jello from cooking the top of the cake while still being warm enough to absorb into the crumb.

Carefully pour the jello mixture evenly over the entire surface of the poked cake, allowing it to seep into all the holes. Cover the cake with plastic wrap and refrigerate for at least 3 hours, or until the jello is completely set and firm to the touch. This chilling time is essential—it allows the jello to set properly and the flavors to meld with the cake.

About 30 minutes before serving, remove the whipped topping from the refrigerator (it should be fully thawed for the smoothest spread). Fold in the vanilla extract gently until just combined. Spread the vanilla whipped topping evenly over the chilled cake, then arrange the sliced fresh strawberries on top in an attractive pattern. Serve immediately or keep chilled until ready to serve—the contrast between the cool cake, fluffy topping, and fresh strawberries is best enjoyed soon after assembly.