Step 1

First, brown the butter. In a light-colored saucepan, melt the butter over medium-low heat, swirling the pan occasionally, until it starts to foam. Use a heatproof rubber spatula to scrape the bottom and sides of the pan occasionally to prevent the milk solids in the butter from burning. Cook for 5 minutes, or until the butter smells nutty and is amber with dark flecks at the bottom of the pan. Remove from the heat and immediately pour the brown butter into a liquid measuring cup. Set it on a wire rack to cool while you prep the other ingredients.

Step 2

Make the dough. In a medium bowl, whisk together the flour, baking soda, and salt. In the bowl of a stand mixer fitted with the paddle attachment, combine the sugars.

Step 3

Pour the brown butter over the sugars in the mixer bowl and beat on medium speed until light and fluffy, 2 to 3 minutes, scraping down the bottom and sides of the bowl with a rubber spatula as necessary. Reduce the mixer to low and add the eggs and vanilla and beat until just combined. With the mixer on low, gradually add the dry ingredients and beat until just combined. Scrape down the bottom and sides of the bowl once more, and beat on low for an additional 30 seconds. Increase the mixer to medium-low, add the chocolates all at once, and beat until the chocolate is evenly distributed throughout, about 1 minute.

Step 4

Chill the dough. Line a quarter sheet pan with parchment paper. Use a 4-tablespoon cookie dough scoop to portion the cookie dough into balls, placing the cookie dough balls on the prepared pan as you go. Cover loosely with plastic wrap and refrigerate for at least 30 minutes.

Step 5

Prep your oven and pans. Position a rack in the center of the oven and preheat the oven to 375°F. Line two half sheet pans with parchment paper. Place the chilled cookies at least 3 inches apart on the prepared sheet pans.

Step 6

Bake the cookies. Bake one pan at a time for 10 minutes, or until the edges have set but the centers are still gooey. Cool the cookies on the pan on a wire rack for 20 minutes, or until the edges and bottoms of the cookies have set and feel firm to the touch. Repeat with the remaining cookie dough (or freeze it to bake later).

Step 7

Serve and store. Serve warm or at room temperature. The cookies can be stored in an airtight container or zip-top bag at room temperature for up to 3 days.