01 - Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper, allowing overhang on sides for easy removal later.
02 - In a medium bowl, whisk together flour, baking powder, and salt until evenly distributed. Set aside.
03 - In a large bowl, beat softened butter and granulated sugar with electric mixer on medium speed until light and fluffy, approximately 2-3 minutes.
04 - Add egg, egg yolk, vanilla extract, and almond extract to butter mixture. Beat until fully incorporated and smooth.
05 - Gradually add flour mixture to wet ingredients, mixing on low speed until just combined. Avoid overmixing to prevent tough bars.
06 - Press dough evenly into prepared baking pan using spatula or lightly floured hands to create uniform thickness.
07 - Bake for 18-20 minutes until edges are lightly golden brown but center remains soft. Remove from oven and cool completely in pan on wire rack.
08 - While bars cool, beat butter until creamy. Gradually add powdered sugar, milk, vanilla extract, and salt. Continue beating until fluffy and spreadable consistency is achieved.
09 - Spread frosting evenly over completely cooled bars. Immediately top with red, white, and blue sprinkles while frosting is still moist for better adhesion.
10 - Using parchment paper overhang, lift bars from pan. Cut into 16 equal squares. Serve immediately or store in airtight container.