Heat oven to 350°F. Line two baking sheets with parchment.
Whisk flour, cornstarch, baking powder, baking soda, salt, and cinnamon in a bowl.
Cream butter, granulated sugar, and brown sugar until light and fluffy, about 2 minutes.
Beat in the egg, yogurt, milk, vanilla, and lemon zest until smooth.
Stir dry ingredients into the bowl just until combined. Do not overmix.
Toss blueberries with the teaspoon of flour if using, then gently fold into the dough.
Scoop heaping tablespoon portions onto sheets, spacing 2 inches apart. Sprinkle with turbinado sugar.
Bake 11–13 minutes until edges set and tops look matte. Rotate pans once halfway.
Cool 5 minutes on the sheet, then transfer to a rack to finish cooling.