1/4 tsp xanthan gum if using a flour which doesn't contain xanthan
1/2 cup frozen corn (optional but recommended!)
Turn oven on to 400 degrees F. Put butter in a cast iron skillet and allow to sit in the oven while it is preheating, until the butter is melted.
Whisk together sugar, egg, and milk.
Add dry ingredients and corn and stir with a spoon until batter is mostly smooth (a few small lumps is OK).
Add melted butter from skillet and stir until combined.
Pour batter into the preheated skillet and bake for 18-20 minutes, until edges are golden brown and/or toothpick inserted in center comes out clean.
This recipe is very forgiving, and has worked well for us with a variety of gluten free flours. Just be sure you stir the flour, scoop it into a measuring cup, and level off with the flat side of a knife. This method will ensure you don't get too much flour in the recipe, which would lead to dense and/or gritty cornbread.
Flours we have used:
Bob's Red Mill 1:1 (not the bean-based)
Recipe by Life After Wheat at https://thereislifeafterwheat.com/2016/05/gluten-free-skillet-cornbread/