Preheat the oven to 350°F. Line baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking soda, baking powder, and salt.
In a large bowl, beat the softened butter and sugar together until light and fluffy.
Add the egg and vanilla extract and mix until combined.
Gradually add the dry ingredients, mixing until just combined.
Add milk 1 tablespoon at a time, until the dough holds together and is easy to scoop.
Scoop tablespoon-sized balls of dough and roll them in granulated sugar.
Place them 2 inches apart on prepared baking sheets.
Bake for 8-10 minutes or until the edges are set and the centers are still soft.
Let cookies cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.