1-Preheat oven: Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper for even baking.

2-Melt butter: Melt the butter and cool it in the refrigerator for about 10 minutes to achieve a chewier texture.

3-Whisk dry ingredients: In a bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt until fully combined.

4-Whisk sugar and lemon zest: In a large bowl, whisk the granulated sugar and lemon zest until it resembles wet sand, releasing the citrus oils for maximum flavor.

5-Add butter: Whisk the cooled melted butter into the sugar mixture until well blended.

6-Add eggs and vanilla: Add the egg, egg yolk, and vanilla extract; mix until smooth and creamy.

7-Combine wet and dry: Stir the dry ingredients into the wet ingredients until just combined, then gently fold in the blueberries to keep them intact.

8-Scoop dough: Using a medium cookie scoop, drop dough balls onto the baking sheet, leaving 3 inches of space between them; optionally, roll them in granulated sugar first.

9-Bake: Bake for 10-12 minutes, or until the edges are set and light golden brown.

10-Cool cookies: Cool the cookies on the baking sheet for 3-4 minutes before transferring to a wire rack.