01 - Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper, allowing excess to hang over the sides for easy removal.
02 - In a medium mixing bowl, whisk together flour, baking powder, and salt until thoroughly combined.
03 - In a large bowl, beat the softened butter and granulated sugar with an electric mixer on medium speed until light and fluffy, about 2 to 3 minutes.
04 - Add the egg, egg yolk, vanilla extract, and almond extract (if using) to the creamed mixture. Beat on low speed until fully incorporated.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just blended.
06 - Evenly press the dough into the prepared baking pan using a spatula or your fingertips to reach all corners.
07 - Place the pan in the oven and bake for 18 to 20 minutes until the edges turn light golden but the center remains soft.
08 - Transfer the pan to a wire rack and allow the cookie bars to cool completely in the pan.
09 - In a clean bowl, beat the softened butter until smooth. Gradually add sifted powdered sugar, milk, vanilla extract, and a pinch of salt, continuing to beat until the frosting is light and spreadable.
10 - Once the cookie base has cooled, spread the prepared frosting evenly over the surface.
11 - Finish with an even layer of red, white, and blue sprinkles on top of the frosting.
12 - Use the parchment paper overhang to lift the entire bar from the pan. Cut into 16 equal squares and serve.