The key to these cookies' chewy, gooey appeal is a combination of the bitter chocolate chips and the high-fat butter (look for butters labeled European-style, or indicating 80 percent or more butterfat).
2 ⅛ cups white all-purpose flour ½ tsp. kosher salt ½ tsp.baking soda 12 tbsp. unsalted, high-fat or European-style butter 1 cup light brown sugar, packed ½ cup white sugar 1 large egg 1 large egg yolk 2 tsp. vanilla extract 2 cups dark or bittersweet chocolate chips
1. Preheat oven to 325°, with racks set in the middle of the oven.
2. In a medium mixing bowl, sift together flour, salt, and baking soda. In a stand mixer, cream together butter and sugars until thoroughly blended. Add egg, egg yolk, and vanilla, and mix to incorporate. Add dry ingredients to the bowl with the wet ingredients and mix until just combined. Gently fold in chocolate chips.
3. Divide dough into 1/4 cup portions; roll into balls, transfer to parchment-lined cookie sheets, about 9 cookies per sheet. Bake for about 15 minutes, rotating the pans halfway through. When fully cooked, the outer edges of the cookies should be golden and slightly crisp, while the middle should still be slightly soft.