Heat oven to 350℉.
Spray a 12 inch cast iron skillet with baking spray. Set aside.
Combine chocolate and butter in microwave proof bowl.
Microwave in 15 second increments, stirring well after each, until melted and smooth. Set aside.
In a large bowl, whisk together eggs, sugar, salt, and vanilla.
Whisk in melted chocolate mixture.
Add flour and cocoa powder.
Mix well.
Stir in chocolate chips.
Pour into prepared skillet.
Bake for 40 minutes, or until desired degree of doneness.