01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat softened butter, granulated sugar, and brown sugar until light and fluffy, approximately 2-3 minutes.
04 - Mix in egg and vanilla extract until fully incorporated.
05 - Gradually mix in half the dry ingredients, followed by milk, then remaining dry ingredients.
06 - Gently fold in blueberries and lemon zest, being careful not to crush the berries.
07 - Drop mounds of dough about 2 tablespoons each onto prepared baking sheets, spacing 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 - Let cookies cool on baking sheets for 5 minutes before transferring to wire rack.