01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2–3 minutes.
03 - Incorporate egg and vanilla extract, beating until thoroughly combined.
04 - Whisk together flour, baking powder, and salt in a separate bowl.
05 - Gradually blend dry ingredients into wet mixture, mixing just until combined. Avoid overmixing to prevent tough texture.
06 - Evenly press dough into the prepared baking pan, creating a uniform layer.
07 - Bake for 18–20 minutes until edges are lightly golden and center is set. Cool completely in the pan before frosting.
08 - Beat softened butter until creamy. Gradually add powdered sugar, alternating with milk, beating until smooth and fluffy.
09 - Blend in vanilla extract and pinch of salt. Incorporate food coloring if desired.
10 - Spread frosting evenly over completely cooled cookie bars. Top with sprinkles if using.
11 - Lift bars from pan using parchment paper overhang. Cut into 24 equal squares.