Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

Cream the cold butter with granulated and brown sugar until light and fluffy, about 4 minutes, using an electric mixer.

Add the egg, egg yolk, lemon zest, lemon juice, and optional lemon extract, mixing on low until just combined.

In another bowl, whisk together flour, cornstarch, baking soda, and salt. Gently fold into the wet ingredients until just combined.

Fold in the lemon or white chocolate chips evenly throughout the dough.

Scoop and roll the dough into 6-ounce balls, spacing them on the baking sheet.

Bake for 9 to 11 minutes, checking that the edges are firm and the centers are slightly underbaked.

Cool the cookies on the baking sheet for at least 10 minutes before transferring to a wire rack.