01 -
Preheat the oven to 190°C (375°F) for 20-30 minutes. Line two large baking sheets with parchment paper.
02 -
Melt the butter in a small bowl and place it in the refrigerator to cool for 10 minutes.
03 -
In a medium bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt until well combined.
04 -
In a large mixing bowl, whisk the granulated sugar and lemon zest together until they resemble wet sand.
05 -
Whisk in the cooled melted butter until combined. Then whisk in the egg, egg yolk, and vanilla extract until smooth.
06 -
Stir the dry ingredients into the wet mixture until just combined. Gently fold in the fresh blueberries.
07 -
Using a medium cookie scoop (about 2 tablespoons), portion the dough into balls. If desired, roll the balls in granulated sugar before placing them on the parchment-lined baking sheets, spaced 8 cm (3 inches) apart.
08 -
Bake at 190°C (375°F) for 10-12 minutes, or until the edges are lightly golden.
09 -
Let the cookies cool on the baking sheet for 3-4 minutes before transferring to a wire rack to cool completely.