Do they have the green tops yet? If so, try this:
Radish Top Soup
6 Tablespoons butter
1 cup chopped onions or leeks
8 cups loosely packed radish leaves
2 cups diced peeled potatoes
6 cups liquid (water, chicken stock)
Salt
1/2 cup cream (optional)
Freshly ground pepper
Melt 4 tablespoons butter in a large saucepan, add onions or leeks, and cook until golden, approximately 5 minutes. Stir in radish tops, cover pan, and cook over low heat until wilted, 8-10 minutes.
Meanwhile, cook potatoes until soft in liquid along with 1 teaspoon salt. Combine with radish tops and broth, and cook, covered, for 5 minutes to mingle flavors. Puree finely in a food processor. Add cream if desired. Season to taste with butter, salt and pepper.
If not, try this?
Braised Purple Radishes
20 plump purple or red radishes
1 to 2 Tablespoons butter
2 stalks green garlic, cleaned as you would a leek and chopped, use all the light green part
1 teaspoon chopped fresh thyme
S & P to taste
Trim the leaves from the radishes, leaving a bit of the green stems, and scrub them. Wash the leaves and set aside. Leave smaller radishes whole and halve the larger ones.
Melt 2 to 3 teaspoons of the butter in a small saute pan. Add the shallot and thyme and cook for 1 minute over medium heat. Add the radishes, a little salt and pepper, and water just to cover. Simmer until the radishes are tender, 3 to 5 minutes. Add the leaves and cook until they're wilted and tender, 1 minute more. Remove the radishes to a serving dish. Boil the liquid, adding a teaspoon or two more butter if you like, until only about 1/4 cup remains. pour it over the radishes and serve.
You can do this recipe if you don't have the tops, but I would add a few leaves of arugula or fresh spinach...