Step 1

Brown butter as detailed in my How to Brown Butter post. Allow to cool slightly.

Step 2

In a large bowl, whisk together cooled brown butter and brown sugar until well combined.

Step 3

Add egg and beat well until mixture has lightened in color and thickened. Mix in vanilla extract.

Step 4

In a separate bowl, whisk together flour, cornstarch, and baking soda.

Step 5

Fold dry ingredients into wet ingredients until dough is well combined.

Step 6

Fold in chopped chocolate, including small bits and shards.

Step 7

Cover dough with plastic wrap and place in refrigerator to chill at least one hour, or up to overnight.

Step 8

Use a #30 cookie scoop or spoon 2½ tablespoon-sized balls onto a large baking sheet lined with parchment paper or a silicone baking liner.

Step 9

Preheat oven to 375°F. While oven is preheating, place baking sheet with dough balls into freezer to chill for 10 minutes.

Step 10

Place cookie sheet in oven and immediately reduce oven temperature to 350°F.

Step 11

Bake cookies at 350°F for 12 minutes, or until edges are golden brown. For a more gooey, undercooked interior, remove after 10 minutes.

Step 12

Sprinkle cookies with flaky sea salt, if desired. Let cookies cool for 15 minutes on the cookie sheet, then carefully transfer to a wire rack to cool completely.