Mix Dry Ingredients: In a medium bowl, whisk together flour, baking soda, baking powder, and salt. Set aside.
Cream Butter & Sugar: In a large bowl, beat softened butter and sugar together until light and fluffy.
Add Wet Ingredients: Mix in egg, vanilla extract, and milk until smooth.
Combine: Gradually add the dry ingredients into the wet mixture until a dough forms.
Chill Dough: Cover and refrigerate dough for at least 1 hour to help cookies keep their shape.
Preheat & Shape: Preheat oven to 350°F (175°C). Roll chilled dough into balls (about 1 tablespoon each), then roll in sugar.
Bake: Place on parchment-lined baking sheets and bake for 9–11 minutes, until edges are set but centers look slightly soft.
Cool: Let cookies rest on the baking sheet for 5 minutes before transferring to a wire rack.