Preheat the oven to 350 Fahrenheit.
Grease a 9 inch cast iron skillet and set aside. Combine the butter and 7 ounces of chocolate chips in a bowl. I suggest cubing the butter.
1/2 cup unsalted butter, 7 ounces chocolate chips
Melt in the microwave in 30 second increments, stirring between each until fully melted.
Meanwhile, add the sugar and eggs to a bowl and mix with an electric mixer for about 1 full minute. This will help give that crackly crust.
3/4 cup white sugar, 2 eggs
Add the melted chocolate/butter mixture into the egg/sugar mixture along with the vanilla and beat to combine.
1 teaspoon vanilla extract
Add in the flour, cocoa powder, tapioca starch and salt and fold to combine.
1/3 cup gluten free all purpose baking flour, 3 tablespoons cocoa powder, 1 tablespoon tapioca starch, 1/2 teaspoon salt
Add in an additional 1/2 cup of chocolate chips if desired and mix well.
1/2 cup chocolate chips
Transfer the batter to your prepared skillet and spread the top out smoothly.
Bake for 30-38 minutes or until the top looks set and crackly. If you prefer a more fudgy texture, bake for less time, for more cakey bake for longer.