Preheat the oven to 350 F. Lightly grease an 8 or 9-inch cast iron skillet.
In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth. Add the egg and vanilla extract and whisk until well combined.
Add the gluten free 1-to-1 baking flour, baking soda, and salt. Stir with a rubber spatula until a thick dough forms with no dry streaks remaining. Fold in the chocolate chips.
Press the dough evenly into the prepared skillet. Scatter a few extra chocolate chips on top if desired.
Bake for 22 to 26 minutes until the edges are golden brown and set but the center still looks slightly underdone. It will firm up as it cools.
Let cool for 5 to 10 minutes, then serve warm straight from the skillet with scoops of vanilla ice cream on top.