Roast until the radishes are fork-tender, about 20 minutes.
Top with chopped parsley and serve.
2 tablespoons parsley
Video
Notes
While raw radishes have a sharp flavor, cooked ones are mild. So you should salt them liberally and season them well. If you prefer bolder flavors, add more seasonings or sprinkle the radishes with Parmesan cheese before roasting. I especially like using onion powder, chili powder, and dried thyme. I add ½ teaspoon of each. That said, seasonings, especially salt, are just guidelines, so please adjust to taste.
If you're after bolder flavors, another option that I tried and liked is to cook the radishes in olive oil and balsamic vinegar - a tablespoon of each - instead of butter.
If the radishes are large, they'll need to stay longer in the oven - up to 30 minutes.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. Reheat them in the microwave at 50% power. I also like them cold, straight out of the fridge.