Prepare Sugar Cookie Bars

Preheat your oven to 350°F (175°C). Line a 10x15-inch rimmed baking sheet with parchment paper.

In a large bowl, beat together the softened butter and cream cheese until smooth. Add granulated sugar and continue beating until light and fluffy.

Mix in the egg and vanilla extract until well combined.

In a separate bowl, combine the flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the butter mixture, mixing until just combined.

Press the dough evenly into the prepared baking sheet and bake for 23-28 minutes, or until the edges are lightly golden. Allow the bars to cool completely before frosting.

Make the Buttercream Frosting

In a mixing bowl, beat the softened butter until smooth. Add the shortening and continue mixing until creamy.

Gradually mix in the powdered sugar and vanilla extract. Add enough milk or cream to reach a spreadable consistency.

Once the cookie bars have cooled, spread the frosting over the top. Add sprinkles if desired.