Preheat oven to 350° F and grease cast iron skillet with cooking spray.
Using a hand mixer, combine butter and sugars in a large bowl until creamy. Add beaten egg with vanilla, flour, baking soda and salt mixed together. Fold in 1 cup of chocolate chips.
In an even layer, spread dough into skillet. Add remaining 1/4 cup chocolate chips on top. Bake until edges are golden brown for 20 to 24 minutes.
Serve warm with ice cream, caramel or chocolate syrup.