01 - Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper, allowing an overhang for easy removal.
02 - In a medium bowl, whisk together flour, baking powder, and salt; set aside.
03 - In a large mixing bowl, beat softened butter and granulated sugar with an electric mixer until light and fluffy, about 2 to 3 minutes.
04 - Beat in the egg, egg yolk, vanilla extract, and almond extract if using, until fully blended.
05 - Gradually add dry ingredients to the wet mixture, mixing until just incorporated and no flour streaks remain.
06 - Transfer dough to the prepared baking pan and spread evenly using a spatula or fingers.
07 - Bake for 18 to 20 minutes until edges are lightly golden and center remains soft.
08 - Remove pan to a wire rack and let bars cool completely in the pan.
09 - In a mixing bowl, beat softened butter until creamy. Gradually add sifted powdered sugar, then milk, vanilla, and a pinch of salt, beating until fluffy and smooth. Adjust milk for desired consistency.
10 - Once bars are fully cooled, spread frosting evenly over the surface.
11 - Top with red, white, and blue sprinkles for a festive finish.
12 - Lift bars from pan using parchment paper overhang. Slice into 16 squares and serve.