Preheat oven to 375 degrees F and line a baking sheet with parchment paper. Set aside.
In a small bowl, add flour, baking powder, cornstarch, salt and baking soda. Mix well and set aside,
In a separate bowl, add sugar and lemon zest and mix well. Stir in butter, egg, and egg yolk and mix well. Stir in flour mixture just until combined. Fold in blueberries.
Using a 2 tablespoon portion scoop, scoop dough into prepared baking sheet 3" apart and bake for 10-12 minutes or until the edges of the cookies just begin to brown. Let stand on the baking sheet for 3 minutes and place on a wire rack to cool completely.