Preheat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.

In a medium bowl, whisk together the flour, baking powder, and salt.

In a large bowl, beat the softened butter and granulated sugar until light and fluffy, about 2 to 3 minutes.

Add the egg, vanilla extract, almond extract, and sour cream, then mix until smooth.

Gradually add the dry ingredients to the wet ingredients and mix just until combined.

Press the dough evenly into the prepared pan in a thin, even layer.

Bake for 18 to 22 minutes, or until the edges are lightly golden and the center is set. Do not overbake.

Allow the bars to cool completely in the pan.

To make the frosting, beat the softened butter until creamy. Add the powdered sugar, milk, and vanilla extract, then beat until smooth and fluffy.

Divide the frosting into three portions. Leave one portion white, tint one portion red, and tint one portion blue with gel food coloring.

Spread or pipe the frosting over the cooled bars in patriotic stripes or swirls, then top with red, white, and blue sprinkles.

Cut into bars and serve.