Once the oven is preheated, carefully remove the cast iron skillet and add 2 tablespoons of unmelted butter. Let it melt and turn golden (about 2 minutes).
Pour the batter into the hot skillet and return it to the oven. Bake for 30–45 minutes, checking for doneness with a toothpick after 30 minutes. The toothpick should come out clean or with a few crumbs when ready.
If you don't have a cast iron skillet, a glass or ceramic baking dish can be used instead. You may need to adjust the baking time slightly.