1 2/3cups chocolate chips, plus extra for sprinkling
Preheat oven to 350F.
Place butter in an (approx. 10″) cast iron skillet and set over medium-low to medium heat. Cook until the butter melts, foams up, and turns golden-brown, whisking occasionally. Remove from heat promptly.
Meanwhile, in a medium bowl, whisk together the flour, baking soda, and salt.
Transfer browned butter to a separate, large bowl and add brown sugar. Whisk together until well-combined. Add whole egg and yolk one at a time, whisking in until incorporated. Mix in vanilla.
Add the dry ingredients to the wet and fold in until partially incorporated. Add the chocolate and continue to fold just until all ingredients are evenly combined.
Transfer batter to skillet and press in to cover surface of pan in a flat layer. Sprinkle extra chocolate chips on top, if desired. Bake in preheated oven for 20-25 minutes, until edges are golden.
For a gooier cookie, cool briefly and serve while still warm from the oven. Otherwise, cookie can be covered with plastic wrap once completely cool and kept at room temperature until ready to serve.