Preheat oven to 450°.
In a medium cast-iron or other oven-safe skillet, combine all ingredients.
Once the oven is at temperature, place the skillet in the oven and roast for 10 minutes. Check the radishes by pricking with a fork—they should be tender. If not, spoon some of the melted butter over the top of the radishes and place in the oven for another 5 minutes, or until they are fork-tender. Serve hot.