4 tablespoons unsalted butter 4 large onions, halved & thinly sliced 1/4 cup sugar salt, to taste 1/2 teaspoon black pepper 6 cups beef stock 1/2 cup port or sherry wine 4 thick slices French bread, toasted 1 cup grated Swiss cheese
Melt butter in large cooking pot. Add the onions and wilt over medium heat, covered, for 20 minutes, stirring occasionally.
Sprinkle the sugar over the onions, stir and cook uncovered until caramelized, about 30 minutes. (Don't cut this process short - it's better if the onions are light brown.) Add salt & pepper.
Add the stock and cook for 30-40 minutes over medium heat. Then add wine and cook an additional 15 minutes.
Preheat broiler, or the oven to 350 degrees F.
Ladle the soup into ovenproof bowls. Top with a slice of toasted bread, and sprinkle cheese on top. Broil or bake until the cheese melts. If you don't want to use the oven, put toast & cheese in bowl first, and ladle soup over.