1. Preheat and Prepare Pan:

Preheat your oven to 350°F (175°C).

Line the bottom of a 15x10x1-inch baking sheet with parchment paper.

Coat the parchment paper and the sides of the pan with cooking spray.

2. Combine Dry Cake Ingredients:

In a large bowl, combine the white cake mix, strawberry gelatin powder, granulated sugar, and all-purpose flour. Whisk them together briefly to distribute everything evenly.

3. Add Wet Cake Ingredients:

Add the water, canola oil, and beaten eggs to the dry ingredients.

Beat with an electric mixer on low speed for 30 seconds, just to moisten everything.

Increase the speed to medium and beat for 2 minutes, scraping the bowl occasionally.

4. Fold in Strawberries:

Gently fold the finely chopped fresh strawberries into the batter using a rubber spatula.

5. Bake the Cake:

Pour the batter into the prepared baking sheet. Spread it evenly to the corners.

Bake for 15-16 minutes, or until a toothpick inserted into the center comes out clean. Keep an eye on it, as sheet cakes bake quickly!

6. Cool the Cake Completely:

Let the cake cool completely in the pan on a wire rack. Ensure it’s fully cool before frosting.

7. Prepare Strawberries for Frosting:

Place the ½ cup of fresh strawberries for the frosting in a food processor or blender.

Pulse or blend until smooth. Set aside.

8. Make the Mascarpone Frosting:

In the bowl of a stand mixer (or using a hand mixer and a large bowl), beat the softened butter and room temperature mascarpone cheese together until light and fluffy, about 3-5 minutes.

Beat in the salt and the pureed strawberries until combined.

Gradually beat in the confectioners’ sugar on low speed until just incorporated.

Increase the speed to medium-high and beat until the frosting is smooth and fluffy.

9. Frost and Garnish:

Spread the strawberry mascarpone frosting evenly over the cooled cake.

Garnish with additional fresh strawberry slices, if desired.

10. Serve:

Slice the cake into squares and serve. Store leftovers covered in the refrigerator. Enjoy!