01 - Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper, allowing overhang on two sides for easy removal.
02 - Whisk together flour, baking powder, and salt in a medium bowl until thoroughly combined. Set aside.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
04 - Mix in egg, egg yolk, vanilla extract, and almond extract until fully incorporated into the butter mixture.
05 - Gradually add the flour mixture to the wet ingredients, mixing until just combined. Do not overmix.
06 - Press dough evenly into prepared pan using a spatula or hands. Bake for 18-20 minutes until edges are lightly golden and center appears set.
07 - Let bars cool in pan on wire rack until completely room temperature before frosting.
08 - Beat softened butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt, beating until smooth and spreadable.
09 - Spread frosting evenly over cooled bars. Immediately top with red, white, and blue sprinkles.
10 - Lift bars from pan using parchment overhang. Cut into 16 equal squares and serve.