3 Tbls unsalted butter
4 large onions (about 2.5 lbs total), halved & thinly sliced
1 tsp sugar
2 Tbls all-purpose flour
2, 14.5 oz cans beef broth (not condensed)
1/4 cup sherry or red wine
6, 1/2″ thick slices French bread, cut on a slight diagonal
1/4 lb Gruyère or Swiss cheese
1. Melt butter in a large, deep pot over medium heat. Add onions & stir to coat with butter. Cover; cook 15 minutes, stirring occasionally until onions are very soft and begin to turn golden brown.
2. Uncover and increase heat to med-high. Stir in sugar. Cook, uncovered, 6-7 minutes, stirring often. Sprinkle with flour & cook 1 minute longer. Stir in broth, sherry or wine & 1 cup water. Simmer, uncovered, for 5 minutes.
3. Heat broiler. Spread bread slices onto a baking sheet; toast under broiler for 1-2 minutes per side (or use a toaster). Set aside. Place 6 oven-proof bowls or crocks onto baking sheet. Divide soup evenly among bowls (about 1 cup in each).
4. Use a vegetable peeler or cheese plane to thinly slice pieces of cheese. Place slice of toast on each serving of soup, top with cheese. Heat under broiler for 3 minutes, or until cheese is melted & bubbly. Carefully remove from oven & serve warm.