Preheat oven to 350°F.

In a medium bowl, sift together the flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer, cream together butter, confectioners' sugar, and granulated sugar on medium speed for at least 2 minutes, scraping down the sides as needed.

Add the egg, vanilla, and milk and blend until smooth and fluffy (about 30 seconds).

Add the flour mixture and mix on low until fully incorporated.

Chill the batter for 10-15 minutes.

Scoop 1/2 teaspoon-sized dollops of the batter (about 1 inch apart) onto a baking sheet lined with parchment.

Bake 12-15 minutes, rotating pan halfway through baking. Cookies will be golden brown.

Allow to cool completely before serving.