01 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl; set aside.
02 - Beat softened butter and granulated sugar with an electric mixer until light and fluffy, approximately 2 to 3 minutes.
03 - Add egg and vanilla extract to the butter mixture; beat until fully combined.
04 - Mix in the whole milk until evenly distributed.
05 - Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined; avoid overmixing.
06 - Cover the dough and refrigerate for at least 1 hour or up to overnight for optimal texture.
07 - Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper.
08 - Scoop tablespoon-sized portions, roll each into balls, then coat evenly with remaining granulated sugar.
09 - Place dough balls 2 inches apart on prepared baking sheets.
10 - Bake for 9 to 11 minutes until cookies are set and edges begin to turn golden.
11 - Allow cookies to cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.