01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together the flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat the softened butter, granulated sugar, and brown sugar in a large bowl until light and fluffy, about 2-3 minutes.
04 - Add the egg and vanilla extract. Mix until fully incorporated.
05 - Gradually mix in half the dry ingredients, followed by the milk, then the remaining dry ingredients.
06 - Gently fold in the blueberries and lemon zest, being careful not to crush the berries.
07 - Drop mounds of dough using a cookie scoop or tablespoon, about 2 tbsp each, onto prepared baking sheets. Space about 2 inches apart.
08 - Sprinkle tops with coarse sugar if desired.
09 - Bake for 12-14 minutes until edges are lightly golden and centers are set.
10 - Allow cookies to cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.