In a small saucepan, brown the butter over medium heat until golden and nutty, then cool to room temperature.

In a large bowl, whisk the cooled brown butter with brown sugar and granulated sugar until well combined.

Add the egg, egg yolk, and vanilla extract, whisking until the mixture is pale and glossy.

Sift together the flour, baking soda, cornstarch, and salt in a separate bowl.

Fold the dry ingredients into the wet ingredients until just combined, ensuring no flour streaks remain.

Fold in the chocolate chunks manually.

Scoop dough into large 3-ounce balls and place on a tray.

Cover and refrigerate the dough balls for 24 hours to hydrate the flour and deepen the flavor.

Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.

Space cookie dough balls 3 inches apart on the baking sheet to allow for spreading.

Bake for 10-12 minutes until edges are set and golden but centers remain slightly soft.

Allow to cool on the baking sheet for 10 minutes before transferring to a wire rack.