Preheat your oven to 350°F. This is important as it sets the stage for even baking. A well-preheated oven helps your cake rise beautifully!
Begin by adding your strawberries to a blender or food processor. Blend them until smooth, as you'll need 1 cup of pureed strawberries for the cake batter and an additional ¼ cup for the frosting. The puree should be a vibrant pink color, indicating ripe strawberries.
In a large bowl, mix together the cake mix, eggs, and vegetable oil until well combined. You'll want a smooth batter with no lumps. The mixture should be thick and slightly glossy.
Add the strawberry jello mix and 1 cup of the strawberry puree to the batter. Stir well until everything is incorporated. The batter should now have a lovely pink tint, thanks to the strawberries and jello.
Pour the batter into a greased 9x13-inch pan. Spread it evenly with a spatula to ensure it cooks uniformly. Look for any air bubbles and gently tap the pan to release them.
Place the cake in the preheated oven and bake for 30 minutes. You'll know it's ready when a toothpick inserted in the center comes out clean. The top should be lightly golden.
Once baked, let the cake cool in the pan for about 10 minutes. Then transfer it to a wire rack to cool completely. This step is crucial to prevent a soggy bottom.
While the cake is cooling, prepare the frosting. In a mixing bowl, cream together the butter and cream cheese until smooth and fluffy. This should take about 2 to 3 minutes. The mixture should be pale and creamy.
Add the vanilla extract, powdered sugar, and the remaining ¼ cup of strawberry puree to the frosting mixture. Mix until combined and fluffy. The frosting should be thick enough to spread easily but not too stiff.
Once the cake has cooled completely, frost the top with the strawberry frosting. Use a spatula to spread it evenly. I love to decorate with additional sliced strawberries for an extra touch. Enjoy your delicious creation!