1 3/4 cups flour
1/2 tsp baking soda
1 3/4 sticks unsalted butter
1/2 cup sugar
3/4 packed brown sugar
1 tsp salt
1 tsp vanilla
1 egg yolk
1 1/4 cups chocolate chips
Preheat an oven to 375 degrees.
Sift together flour and baking soda, set aside.
Place 10 tablespoons butter in a heavy-bottomed saucepan or skillet. Heat over medium-high until the butter melts. Continue to cook until the butter is a deep golden brown, swirling the pan constantly (~1-3 minutes). Pour thebrown butter into a large bowl, and immediately add the remaining 4 tablespoons of reserved butter. Let sit, swirling occasionally, until the remaining butter has melted.
When all the butter has melted, add the sugars, salt and vanilla to the bowl, and whisk to combine. Add the egg and egg yolk. Whisk until the mixture is smooth, ~30 seconds, and then let sit for 3 minutes. Repeat the whisking and resting two more times. The sugars will begin to dissolve, and the mixture will become thicker, shiny and lighter in color.
Stir in the flour mixture until just combined, and fold in the chocolate chips. Scoop balls of dough onto a prepared cookie sheet, using 2-3 tablespoons of dough (depending on how large you like your cookies). Bake, one sheet at a time, until the edges are beginning to get golden, but the centers are still puffy and soft (8-14 minutes, depending on cookie size and oven temperature).
Cool on a rack.