In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Preheat the oven to 350°F (175°C).

Roll out the dough on a floured surface to about 1/4 inch thick.

Use a star-shaped cookie cutter to cut out cookies and place them on a baking sheet lined with parchment paper.

Bake for 8-10 minutes or until the edges are lightly golden.

Allow cookies to cool completely on a wire rack.

Once cooled, use royal icing to decorate the cookies in a flag pattern, using blue icing for the stars and red icing for the stripes.

Sprinkle blue and red sprinkles on the appropriate areas for added decoration.