6 medium red or white onions (3 1/2 lb)
3 tablespoons fine-quality extra-virgin olive oil (preferably Tuscan)
10 fresh thyme sprigs or 1 teaspoon dried thyme
Fine sea salt to taste
1/2 cup Chianti or other dry red wine
1/4 cup water
Preheat oven to 400°F. Cut a slice from both ends of each onion, then halve onions crosswise. Discard outer layers from onions, leaving about a 2 1/2-inch diameter.
Arrange onions, trimmed ends down, in an oiled 13- by 9-inch baking pan. Drizzle with oil.
Remove leaves from 2 thyme sprigs and sprinkle over onions. Season with sea salt and pepper, then scatter remaining 8 sprigs over onions. Pour wine over onions.
Bake, uncovered, in middle of oven, basting with pan juices twice during baking, 40 minutes. Add water to pan and bake until onions are browned and tender, about 50 minutes more. Serve hot or at room temperature.