Preheat the oven to 375 F (190 C) and line a large baking sheet with parchment paper.

In a small bowl, melt the butter and cool in the fridge for about 10 minutes.

In another bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt until well combined.

In a large mixing bowl, whisk the sugar and lemon zest together until they are the consistency of wet sand. Whisk in the cooled melted butter until well combined. Then, whisk in the egg, egg yolk, and vanilla extract until smooth.

Stir the dry ingredients into the wet until just combined. Gently stir in the fresh blueberries until combined.

Using a medium cookie scoop, scoop the cookie dough into balls. If rolling in sugar, roll the cookie dough in the sugar and place onto the lined baking sheet about 3 inches apart.

Bake at 375 F (190 C) for 10-12 minutes or until the edges of the cookies are set and are a light golden brown.

Cool the cookies on the baking sheet for 3-4 minutes. Then transfer them to a cooling rack to cool completely.