There's no cheating on the caramelization process using brown sugar in this recipe. It takes time -- from half an hour to an hour -- but it's worth it. The onions don't require constant attention, but you should stir occasionally. To make things easier, you can caramelize the onions ahead of time and then continue with the soup later in the day.
I always slice the onions by hand even though I know my eyes will burn like crazy and stream with tears. You can feel free to use a food processor if you'd like to avoid all that. As for me, I really like the finished product when I slice the onions by hand and somehow, from one time to the next I always remember how delicious the soup was and I forget the pain.
2 Tbsp. butter
2 Tbsp. olive oil
5 large onions, thinly sliced
3 Tbsp. flour
8 cups beef stock
1/2 tsp. dried thyme
Salt and pepper to taste
6-8 thick slices french bread, toasted
2 cups grated Swiss cheese (more or less to taste)
1. Heat butter and oil in a large skillet over medium heat. Add sliced onions and reduce heat to medium-low. Cover (this helps with the burning-eyes aspect and also speeds things up a bit. Just don't get all out-of-sight-out-of-mind about it) and cook onions, stirring occasionally, until well caramelized, half an hour to an hour. While you wait, you can toast the bread and grate the cheese. Maybe make a nice salad.
2. Sprinkle flour over onions; cook, stirring constantly, two minutes.
3. Add stock, salt and pepper. Crush the thyme between your fingers and add. Bring soup to a boil, then reduce heat and simmer 30 minutes. Taste and adjust seasonings as needed.
4. Preheat broiler. Ladle soup into heatproof bowls. Place one slice bread on top of soup, sprinkle with grated cheese. Place bowls on a rimmed baking sheet and slide them under the broiler. Broil until cheese is bubbling and golden brown.