Preheat the oven to 350°F (175°C). Line two large baking sheets with parchment paper.

In a medium bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt. Set aside.

In the bowl of a stand mixer, combine the brown sugar, granulated sugar, and lemon zest. Mix on high speed for 2 minutes to release the oils from the zest and infuse the sugar with lemon flavor.

Add the softened butter to the sugar mixture. Continue mixing until light and fluffy, about 2 minutes.

Add the eggs one at a time, beating well after each addition. Stir in the lemon juice and vanilla extract.

Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid overmixing to ensure a soft texture.

Gently fold in the fresh blueberries, being careful not to crush them.

Using a medium cookie scoop, drop balls of dough onto the prepared baking sheets, spacing them at least 2 inches apart.

Bake for 12-15 minutes, or until the edges are lightly golden and the centers are set.

Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.