Start to finish: 1 hour
1 3/4 cups (8 3/4 ounces) all-purpose flour
1/2 teaspoon baking soda
12 tablespoons unsalted butter
3/4 cup packed (5 1/4 ounces) dark brown sugar
1/2 cup (3 1/2 ounces) granulated sugar
2 teaspoons vanilla extract
1 teaspoon salt
1 large egg plus 1 large yolk
1 cup (6 ounces) semisweet chocolate chips
Adjust oven rack to upper-middle position and heat oven to 375 F. Whisk flour and baking soda together in bowl.
Melt 9 tablespoons butter in 12-inch cast-iron skillet over medium heat. Continue to cook, stirring constantly, until butter is dark golden brown and has nutty aroma, about 5 minutes. Transfer browned butter to large bowl and stir in remaining 3 tablespoons butter until melted. Whisk in brown sugar, granulated sugar, vanilla, and salt until incorporated. Whisk in egg and yolk until smooth with no lumps, about 30 seconds.
Let mixture stand for 3 minutes, then whisk for 30 seconds. Repeat process of resting and whisking 2 more times until mixture is thick, smooth, and shiny. Using rubber spatula stir in flour mixture until just combined, about 1 minute. Stir in chocolate chips.
Wipe skillet clean with paper towels. Transfer dough to now-empty skillet and press into even layer with spatula. Bake until cookie is golden brown and edges are set, about 20 minutes, rotating skillet halfway through baking. Using potholders, transfer skillet to wire rack and let cookie cool for 30 minutes. Slice cookie into wedges and serve.
Nutrition information per serving: 488 calories; 222 calories from fat; 25 g fat (15 g saturated; 1 g trans fats); 96 mg cholesterol; 384 mg sodium; 65 g carbohydrate; 2 g fiber; 42 g sugar; 5 g protein.
For more recipes, cooking tips and ingredient and product reviews, visit https://www.americastestkitchen.com. Find more recipes like Chocolate Chip Skillet Cookie in “The Perfect Cookie .”
America’s Test Kitchen provided this article to The Associated Press.