01 - Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - Whisk flour, baking powder, and salt in a medium bowl until evenly blended.
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.
05 - Gradually fold in flour mixture, mixing just until dough comes together. Avoid overmixing.
06 - Press dough evenly into prepared pan. Bake for 18-20 minutes until edges are lightly golden and center remains soft.
07 - Let bars cool in pan on wire rack until completely room temperature before frosting.
08 - Beat butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt, mixing until fluffy 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.