01 - Preheat oven to 350°F. Line a 9x13-inch baking pan or baking sheet with parchment paper.
02 - In a large mixing bowl, beat together softened butter and granulated sugar with an electric mixer until light and fluffy. Incorporate the egg and vanilla extract, blending thoroughly.
03 - In a separate bowl, whisk flour, baking powder, and salt. Gradually add dry mixture to wet mixture, mixing until a uniform dough forms.
04 - Press dough evenly into prepared pan to a 1/4-inch thickness, ensuring edges are smooth.
05 - Bake for 13 to 15 minutes, or until crust edges turn golden. Remove from oven and allow to cool completely in the pan.
06 - Beat softened cream cheese and butter until smooth. Add powdered sugar and vanilla, mixing to achieve a creamy consistency.
07 - Spread cream cheese frosting evenly over the entirely cooled cookie crust using a spatula.
08 - Arrange blueberries in the top left to symbolize stars. Layer sliced strawberries and raspberries in rows for the red stripes, leaving the frosting exposed for white stripes.
09 - Refrigerate the pizza for at least 30 minutes to set before slicing and serving.