Preheat the oven to 350°F (175°C).
Grease and line a baking pan with parchment paper.
In a mixing bowl, whisk together the flour, baking powder, and salt.
In another bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the egg and vanilla extract to the butter mixture and mix until combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Spread the batter evenly into the prepared baking pan.
Bake for 20-25 minutes, or until the edges lightly golden.
Let the bars cool completely in the pan before frosting.
Prepare the frosting by mixing powdered sugar and milk until smooth.
Frost the cooled bars and add food coloring if desired.
Cut into squares and serve.
