Preheat your oven to 375°F and line two baking sheets with parchment paper. If your butter is still cold, take it out now to let it soften to room temperature.
Lightly toss the blueberries in a small amount of flour. This helps keep them from sinking to the bottom of the cookies and prevents them from bursting during mixing.
In a large mixing bowl, beat the softened butter with both brown and granulated sugar until light and fluffy. Add the eggs one at a time, then mix in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt. Add this dry mixture to the wet ingredients in batches, alternating with the milk. Mix gently—do not overmix.
Gently fold in the floured blueberries with a spatula. Drop large spoonfuls of dough onto the prepared baking sheets, leaving enough space between each cookie.
Bake for 13 minutes or until the edges are set and lightly golden while the centers remain soft. Let cookies rest on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
