4 tbsp butter 4 large sweet onions—cut halved & thinly sliced
Melt butter in large soup pot. Add onions and sauté over medium-low heat covered, 20 min. Stir occasionally.
Sprinkle the sugar over onions. Toss and cook uncovered until caramelized, about 10 min. Sprinkle with salt and pepper.
Add 3 cups of beef stock simmer 15 min, add port wine and last 3 cups of beef stock, simmer 30-40 min.
Preheat broiler, divide soup into 4 ovenproof bowls. Top with a slice of toasted French bread. Sprinkle with cheese. Place under broiler until cheese melts.