01 - Preheat your oven to 350°F. Line a 9x13 inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a large bowl, cream together butter and granulated sugar until light and fluffy, about 2-3 minutes.
03 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
04 - In a separate bowl, whisk together flour, baking powder, and salt.
05 - Gradually add the dry ingredients to the wet mixture, mixing just until combined.
06 - Spread the dough evenly into the prepared pan. Use a spatula or your hands to smooth the top.
07 - Bake for 18-22 minutes, until the edges are lightly golden but the center is still soft. Do not overbake.
08 - Let cool completely in the pan on a wire rack.
09 - For the frosting, beat butter until creamy. Gradually add powdered sugar, then mix in milk and vanilla until smooth. Add food coloring if desired.
10 - Spread the frosting evenly over cooled bars. Top with sprinkles if using.
11 - Lift bars out using parchment overhang, cut into squares, and serve.