Step 1

Let 1 large egg and 1 large egg yolk sit on the counter until room temperature.

Step 2

Melt 1 1/2 sticks unsalted butter in a small saucepan over medium heat until it begins to foam and bubble, about 4 minutes. Swirl the pan occasionally. About 2 minutes later when the cracking sounds stop, continue to swirl the pan or stir with a heatproof spatula until brown bits start to form at the bottom and the butter starts to smell nutty. When the bits are amber in color and the butter is light brown, immediately remove from the heat.

Step 3

Pour into a large heatproof bowl, scraping all the browned solids into the bowl. Let cool until warm to the touch, about 15 minutes. Meanwhile, chop 8 ounces semi-sweet chocolate into 1/4-inch chunks (about 1 1/2 cups), or measure out 1 1/2 cups chocolate chips.

Step 4

Add 1 cup packed dark brown sugar and 1/3 cup granulated sugar to the browned butter and whisk to combine. Add the egg, egg yolk, 1 tablespoon vanilla extract, and 3/4 teaspoon kosher salt. Whisk until smooth and glossy.

Step 5

Add 1 3/4 cups all-purpose flour and 1/2 teaspoon baking soda. Stir with a flexible spatula or wooden spoon until the flour is not yet fully absorbed but mostly incorporated. The dough will look darker and dense unlike most cookie doughs – this is just because of the brown butter!

Step 6

Reserve 1/4 cup chopped chocolate or chocolate chips for topping the cookies. Add the remaining chocolate to the dough and stir to combine. If the dough is firm enough to scoop, you can do it now. If the dough is too soft, cover the bowl and freeze until the dough is firm enough to scoop, about 15 minutes.

Step 7

Line a large plate or baking sheet with parchment paper. Scoop the dough out with a 2-inch cookie scoop or roll into 20 (about 3 rounded tablespoons or 50 grams each) portions, and place on the lined plate or pan. Press the remaining 1/4 cup chocolate into the tops of the cookie dough. Gently flatten each dough ball with the bottom of a drinking glass or measuring cup until about 1/2-inch thick. Lightly cover and refrigerate overnight.

Step 8

Arrange 2 racks to divide the oven into thirds and heat the oven to 350ºF. Line 2 baking sheets with parchment paper. Place the cookie dough balls on the baking sheets, spacing them evenly apart.

Step 9

Bake until the cookies are light brown and puffed, and the centers look set with no wet spots, 11 to 16 minutes. Immediately sprinkle with flaky salt if desired. Let cool on the baking sheets for 5 minutes, then transfer to a wire rack and let cool completely.