01 - Preheat oven to 350°F. Line a 9x13 inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Beat butter and granulated sugar in a large bowl 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 - Whisk together flour, baking powder, and salt in a separate bowl.
05 - Gradually add dry ingredients to wet mixture, mixing just until combined.
06 - Spread dough evenly in prepared pan. Bake for 18-22 minutes until edges are lightly golden but center is still soft.
07 - Let cool completely in pan on wire rack before frosting.
08 - Beat butter until creamy. Gradually add powdered sugar, then mix in milk and vanilla until smooth. Add food coloring if desired.
09 - Spread frosting evenly over cooled bars. Top with sprinkles if using. Lift out using parchment overhang, cut into squares, and serve.