4 sweet onion, peeled, root and stems ends cut off
1/4 cup balsamic vinegar
1/4 teaspoon salt
1/8 teaspoon black pepper
1 tablespoon butter
Preheat the oven to 400 F. Put the onions and balsamic vinegar in an 8 inch square baking dish. Sprinkle with the salt and pepper. Top each onion with one-quarter of the butter. Cover the baking dish with aluminum foil and bake for 1 hour. Remove the foil, turn the onions over and cook for 30 minutes longer. Drizzle the onions with the pan juices and serve.