Thinly slice one of the onions; finely chop the second. I'm a med pot, melt the butter over med heat. Add the sliced onions, sugar, and 1/4 teaspoon of the salt. Cover and cook until almost soft, bout 10 min. Add the chopped onions, increase the heat to med high, cover, and cook until the onions are well caramelized 10-15 min more.

Stir the beef broth, red wine, thyme, and the remaining 1/4 tsp salt into the pot. Simmer gently for 10 min

Preheat broiler

Ladle the soup into 4 heatproof bowls. Float 1 baguette slice in each bowl and sprinkle the cheese over the top. Cook under the broiler until the cheese is golden and bubbling about 5 min. Season to taste with pepper.