01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing overhang on edges for easy removal.
02 - In a large bowl, beat softened butter and granulated sugar together until light and fluffy, approximately 2-3 minutes.
03 - Mix in the egg and vanilla extract until fully incorporated into the butter mixture.
04 - In a separate bowl, whisk together flour, baking powder, and salt until evenly distributed.
05 - Gradually add dry ingredients to wet ingredients, 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. Remove from oven and cool completely in pan.
08 - Beat softened butter until creamy. Gradually incorporate powdered sugar, alternating with milk, until smooth and fluffy.
09 - Blend in vanilla extract and pinch of salt. Add food coloring if desired.
10 - Spread frosting evenly over completely cooled bars. Sprinkle with decorative toppings if using.
11 - Using parchment overhang, lift bars from pan. Cut into 24 equal squares and serve.