In a saucepan, cut 1 lb (2 sticks) of butter into cubes.

Place the butter in the pan and heat over medium heat.

Watch the butter closely as it melts to prevent burning. Once all the cubes have melted, start whisking or stirring with a spatula.

When the butter is fully melted, it will foam, and you'll notice a nutty aroma. Keep whisking until the butter is evenly heated and browned. Be careful not to let it burn.

Turn off the heat and continue mixing. Transfer the browned butter to a heat-safe bowl and immediately add the remaining cold butter. The cold butter will melt and help cool the browned butter.

In a bowl, combine the browned butter, brown sugar, and white sugar. Use a hand mixer or stand mixer to cream the mixture until smooth (1-2 minutes).

Add the vanilla extract, whole eggs, and egg yolks one at a time, beating well after each addition. Scrape down the sides of the bowl as needed. Beat until the mixture is light and fluffy (about 2-3 minutes).

Divide this mixture in half and place 2 cups in a separate bowl.

In the first bowl, add 2 cups + 2 tablespoons of flour, 1/2 teaspoon baking soda, and 1/2 teaspoon salt. Mix until the flour is combined and there are no streaks. Stir in 1/2 cup milk chocolate chips and 1 cup semisweet chocolate chips.

In the second bowl, add the remaining 1 1/2 cups of flour, cocoa powder, 1/2 teaspoon baking soda, 1/2 teaspoon salt, and instant espresso powder. Gently mix until there are no streaks of flour. Add 1 cup milk chocolate chips and 1/2 cup semisweet chocolate chips. Mix until just combined.

To assemble the cookies:

Use a large ice cream scoop to portion out the chocolate chip dough and chocolate dough separately.

Take one scoop of each dough and squeeze them together. Roll into a ball and place on a baking sheet. Sprinkle the top with flaky sea salt.

Leave enough space on the baking sheet for the cookies to spread. Typically, 4-5 cookies per sheet tray works well.

Bake at 350 degrees Fahrenheit for 14-15 minutes.

Once the cookies are baked, we like to gently press in a few chocolate chips to the top, this is optional. Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a cooling rack to cool completely.