Trim the roots from the radishes, and pare off the greens, leaving ¼ to ½ inch of the stems. (This is mostly for looks, and for the slight flavor the stems bring, but if you want, you can completely trim away the greens.) Soak the radishes in cold water for about 15 minutes to loosen any dirt trapped in the stems. Drain and scrub the radishes. If any are more than 1 inch in diameter, halve them.

Put the radishes in a medium (10-inch) skillet. The skillet should hold them in a single layer. Add the butter, stock or water, sugar, and salt and pepper to taste. Bring to a simmer over medium heat; then cover, reduce the heat to maintain a gentle simmer, and cook until the radishes are tender, 18 to 25 minutes. You should be able to easily pierce them with a small knife.

Remove the lid, shake the pan to roll the radishes around, and continue to simmer until the liquid reduces to a glaze and coats the radishes, another 5 to 10 minutes. (You may need to increase the heat under the pan.) Taste for seasoning. Serve warm.