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.
03 - Beat 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 if using, being careful not to crush the berries.
07 - Drop mounds of dough, about 2 tablespoons each, onto prepared baking sheets, spacing about 2 inches apart.
08 - Sprinkle tops with coarse sugar if desired.
09 - Bake for 12-14 minutes, or until edges are lightly golden and centers are set.
10 - Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.