Set oven to 175°C (350°F).
In a bowl, cream butter and sugar together until smooth and fluffy. Add in the egg and beat until combined.
Mix in baking powder and salt, then gradually fold in flour until a soft dough forms.
Press the dough evenly into a rectangle on a parchment-lined baking tray.
Bake for 12 to 15 minutes or until the edges turn light golden. Let it cool completely.
Once cooled, use a pizza cutter or knife to cut into rectangles.
Cover the cooled cookie base with an even layer of whipped cream.
Place blueberries in the upper-left corner to represent the stars section.
Arrange strawberry slices in horizontal stripes to form the red lines of the flag.
Between the strawberry lines, pipe whipped cream in clean lines to complete the white stripes.
