01 - Preheat the oven to 350°F. Line a 9×13-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
03 - In a large bowl, cream the softened butter and sugar together until light and fluffy, about 2–3 minutes.
04 - Beat in the egg, egg yolk, vanilla, and almond extract (if using) until fully combined.
05 - Gradually add the flour mixture to the wet ingredients, mixing until just combined.
06 - Spread the dough evenly in the prepared baking pan using a spatula or your fingers.
07 - Bake for 18–20 minutes, until the edges are lightly golden but the center is still soft.
08 - Let the bars cool completely in the pan on a wire rack.
09 - Beat the butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt, beating until fluffy and spreadable.
10 - Once the bars have cooled, spread the frosting evenly over the top.
11 - Decorate with red, white, and blue sprinkles. Use the parchment overhang to lift the bars out of the pan. Cut into 16 squares and serve.