Preheat your oven to 350°F. Line a 9 x 13-inch baking pan with parchment paper and lightly coat with cooking spray.

Prepare and bake the vanilla cake according to the package directions. Let the cake cool completely in the pan.

While the cake cools, make the blueberry filling. In a small saucepan over medium heat, combine the blueberries, lemon juice, and granulated sugar.

Cook, stirring occasionally, until the berries burst and the mixture thickens to a jam-like consistency, about 5 to 7 minutes.

Remove from heat and let the mixture cool for about 15 minutes.

Gently fold the whipped topping into the cooled blueberry mixture until smooth and evenly combined.

Make the frosting by beating the softened butter and cream cheese together in a large bowl until creamy and well blended.

Add the powdered sugar, lemon zest, lemon juice, and vanilla extract. Beat until fluffy and smooth, scraping down the sides as needed.

Using the handle of a wooden spoon, poke holes all over the cooled cake, spacing them evenly.

Pour the blueberry mixture over the cake, spreading it so it fills the holes and covers the surface.

Spread the cream cheese frosting evenly over the top.

Garnish with fresh blueberries. Chill for at least 1 hour before slicing and serving.