Preheat the oven to 350°F (175°C). Grease the 9x13 inch baking pan or line it with parchment paper for easy removal.

In a mixing bowl, combine flour, baking powder, baking soda, and salt. Whisk together and set aside.

In a separate mixing bowl, cream the softened butter and granulated sugar until light and fluffy, approximately 2-3 minutes.

Add the egg, vanilla extract, and almond extract (if using) to the butter-sugar mixture. Mix until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Spread the cookie dough evenly into the prepared baking pan using a spatula.

Bake in the preheated oven for about 20 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out clean.

Allow the cookie bars to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

While cooling, prepare the frosting by whisking together powdered sugar, milk, and vanilla extract in a small bowl until smooth.

Once the bars have cooled, spread the frosting over the top and sprinkle with colorful sprinkles if desired.

Cut into bars and serve.