1. Heat oven to 400°. Bring a large pot of salted water to a boil, and carefully add the radishes. Cook until almost fork-tender, about 5 minutes, then drain and let cool.
2. Cut radishes in half and place in a bowl with shallots. Drizzle with oil, and season with salt and pepper; toss to coat.
3. Place vegetables on a parchment-lined rimmed baking sheet, cut sides down. Roast about 15 minutes, until the whites of the radishes are just golden and shallots are beginning to caramelize.