01 - Preheat the oven to 350°F. Line a 9×13-inch baking pan with parchment paper, leaving overhang on the sides for easy removal later.
02 - Whisk together the flour, baking powder, and salt in a medium bowl until well combined. Set aside.
03 - Beat the softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
04 - Mix in the egg, egg yolk, vanilla extract, and almond extract until fully incorporated.
05 - Gradually add the flour mixture to the wet ingredients, mixing until just combined. Do not overmix.
06 - Evenly press the dough into the prepared baking pan using a spatula or your hands, spreading it to the edges.
07 - Bake for 18-20 minutes until the edges are lightly golden while the center remains slightly soft.
08 - Allow the bars to cool completely in the pan set on a wire rack.
09 - Beat the butter until creamy. Gradually add the powdered sugar, milk, vanilla, and salt, beating until the frosting is fluffy and spreadable.
10 - Spread the frosting evenly over the cooled bars. Sprinkle with red, white, and blue sprinkles immediately.
11 - Use the parchment overhang to lift the bars from the pan. Cut into 16 squares and serve.