01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a large bowl, beat the softened butter and granulated sugar with an electric mixer until light and fluffy, about 2-3 minutes.
03 - Add the egg and vanilla extract. Beat until fully incorporated.
04 - In a separate bowl, whisk together the flour, baking powder, and salt until evenly distributed.
05 - Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid overmixing to prevent tough texture.
06 - Press the dough evenly into the prepared pan using clean hands or a spatula, ensuring uniform thickness.
07 - Bake for 18-22 minutes, until edges are lightly golden and the center is set. Be careful not to overbake.
08 - Let the bars cool completely in the pan on a wire rack before frosting.
09 - Beat the butter until creamy. Gradually incorporate powdered sugar, then add milk, vanilla, and salt. Beat until smooth and fluffy, adding more milk if needed for spreadable consistency. Stir in food coloring if desired.
10 - Spread the frosting evenly over the cooled bars. Top with sprinkles if using.
11 - Lift the bars out of the pan using the parchment overhang. Cut into 24 equal squares.