01 - Whisk together flour, baking powder, and salt in a medium bowl and set aside.
02 - Using an electric mixer, beat softened butter and brown sugar until light and fluffy, about 2 to 3 minutes.
03 - Incorporate egg and vanilla extract into the butter mixture until fully combined.
04 - Gradually add dry ingredients to the wet mixture, mixing on low speed until a soft dough forms.
05 - Divide dough in half, shape each into a disc, wrap in plastic, and chill for 20 to 30 minutes.
06 - Preheat oven to 350°F. Line baking sheets with parchment paper.
07 - Roll one disc of dough on a lightly floured surface to 1/4 inch thickness. Cut shapes using cookie cutters and place them 1 inch apart on baking sheets.
08 - Bake for 10 to 12 minutes until edges begin to turn golden. Cool on tray for 5 minutes, then transfer to a wire rack to cool completely.
09 - Whisk powdered sugar, milk, and vanilla extract until smooth and spreadable, adding more milk if needed.
10 - Spread or pipe icing onto cooled cookies and sprinkle with sparkling sugar or edible glitter before the icing sets.