Chocolate Chip Skillet Cookie

3/4 cup (1 1/2 sticks) unsalted butter

1/2 cup firmly packed light brown sugar

1/3 cup granulated sugar 

1 teaspoon vanilla 

1 large egg

1 3/4 cup all-purpose flour 

2 1/2 teaspoons baking powder

1/2 teaspoon coarse kosher salt

2 cups chocolate chips 

Heat oven to 350F. 

Heat a 10-inch cast iron skillet over medium heat. Add butter and heat until foam on top is light brown. Pour into a mixing bowl, then whisk in sugars. Whisk for 1 minute to cool, then whisk in egg and vanilla. In a small bowl, stir together flour, baking powder and salt. Stir into butter mixture, then stir in chocolate chips. 

Pour mixture into skillet and bake until golden brown and set, 25-30 minutes. Let cool 15 minutes before cutting.