Step 1

Preheat oven to 375 degrees F.

Step 2

For the bars, in a large bowl, cream together the butter, granulated sugar and powdered sugar until light and fluffy. Add the eggs and vanilla and mix for 1-2 minutes. Stir in the lemon zest (optional), flour, baking powder and salt. Mix until combined.

Step 3

Lightly grease a 9X13-inch baking pan with cooking spray or line with parchment paper and grease. Press the sugar cookie dough into an even layer in the bottom of the pan.

Step 4

Bake for 10-13 minutes. Don't overbake! The bars should have hardly any color around the edges and barely be set in the middle. Let the bars cool completely before frosting.

Step 5

For the frosting, cream together the butter and powdered sugar until smooth (if the mixture has trouble coming together, add a drop or two of milk). Add in the vanilla, milk or cream, and food coloring (if using), and mix until the frosting is light and fluffy, 1-2 minutes.

Step 6

Spread the frosting over the cooled bars and top with sprinkles.