Preheat the oven to 400 degrees F and stick a large (13-inch) cast iron skillet on a rack in the middle.
Mix the rice flour, cornmeal, sugar, baking powder, and salt together in a mixing bowl.
Melt four tablespoons of butter and allow to cool. In a small bowl, combine the eggs, milk, and melted butter. Add this mixture to the flour mixture and stir until just combined.
Remove the skillet from the oven and add the remaining tablespoon of butter. Swirl until it coats the pan.
Pour the batter into the hot skillet and bake for 15-20 minutes or until a wooden toothpick comes out clean. Serve warm.