01 - Preheat oven to 350°F. Line a baking sheet with parchment paper or use a 9x13-inch baking pan.
02 - In a large bowl, beat together unsalted butter and granulated sugar until light and fluffy. Mix in the egg and vanilla extract.
03 - In a separate bowl, whisk together flour, baking powder, and salt. Gradually add the dry mixture to the creamed mixture, blending until fully incorporated.
04 - Press dough evenly into the prepared pan, creating a crust approximately 1/4 inch thick. Bake for 13–15 minutes or until the edges are barely golden. Allow to cool completely.
05 - Beat softened cream cheese and butter together in a bowl until smooth. Add powdered sugar and vanilla extract, mixing until the frosting is creamy.
06 - Using a spatula, spread the cream cheese frosting over the cooled cookie crust in an even layer.
07 - Arrange blueberries in the upper left corner to represent the stars of the flag. Create red stripes with strawberries and raspberries, alternating with the white frosting to mimic flag stripes.
08 - Refrigerate the assembled dessert for at least 30 minutes to set. Slice and serve chilled.