Brown the butter in a saucepan following the instructions to learn how to brown butter. Let it cool.

Combine flour, baking soda, and salt in a medium bowl and whisk well.

Mix cooled brown butter with both sugars in a large bowl until combined. Add egg, milk, and vanilla, mixing until creamy.

Fold in the flour mixture and mix until combined. Add chocolate chunks and chips, mix until evenly distributed.

Cover the bowl and refrigerate the dough for 1-4 hours.

Preheat the oven to 375°F. Line two large cookie sheets with parchment paper.

Use a cookie scoop to portion dough into 14 pieces, rolling into smooth balls and placing them on baking sheets. Bake for 8-10 minutes.

Let cookies cool on the baking sheet for 2 minutes before transferring to a wire rack. Top with flaky sea salt if desired.