Preheat oven to 375 degrees F. Spray a 9x13 pan with cooking spray.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the sugar, powdered sugar, and butter for about 3 minutes or until light and fluffy. Mix in the vanilla and eggs. Beat until smooth. Scrape down the sides if needed. Add the baking powder and salt and mix until combined. Then slowly add in the flour, mix until just combined.

Using a spatula or your hands, evenly spread the cookie dough into the prepared pan. Bake for 12-14 minutes, do not overbake.

Cool completely.

For the frosting: In a stand mixer fitted with the paddle attachment or in a large bowl using beaters, whip the butter for about 2 minutes, or until it's creamy and lightened in color. Slowly add in the powdered sugar. Add the vanilla extract and heavy cream or milk. Start with 3 tablespoons of cream/milk and add 1 more tablespoon if frosting seems too thick. Beat on medium-high for about 3-5 minutes, stopping to scrape the sides of the bowl once or twice. If using food coloring mix in. Beat on low speed for about 1 minute to help remove any air bubbles.

Spread the frosting over the cooled sugar cookie bars evenly and top with sprinkles. Cut into 24 pieces.

Enjoy!