5medium onionshalved and then sliced about 1/8" thick
3 1/2cupsbeef stock
1 1/2tspkosher salt
1cupgrated Gruyère cheese
Heat the butter in a large soup pot (I used my Dutch oven) over medium heat until it is melted. Add the onions, thyme, and bay leaf.
Cook over medium, stirring frequently, for 15 minutes, or as soon as the onions begin to brown.
Reduce the heat to medium low, cover, and cook for an additional 30-40 minutes, stirring frequently, or until the onions take on a rich brown color. Note: Keep an eye on the amount of liquid in your onions, since they will release liquid as they cook. If your pot lid does not have a steam vent, you may need to uncover your onions on and off to allow some of the moisture to evaporate. Covering it will help keep the onions from burning, but you don't want them to stew in their own juices. Also: Take care not to overcook the onions - this step requires a lot of patience. While turning the heat up will make them brown faster, they will be sautéed rather than caramelized. Caramelization is essential for the onions to release their sugars and get that delicious sweet flavor.
Turn the heat to high and and stir in the sherry to deglaze the pan. Make sure you scrape up any browned bits from the bottom of your pot, since those will make your soup even more delicious! When the sherry has been cooked off, add the beef stock.
Bring to a boil, then simmer for 20 minutes, partially covered. Add salt and pepper to taste and remove the bay leaf.
Place 2 individual oven-safe soup crocks or 4 smaller ramekins on a rimmed baking sheet. Fill each bowl with soup, top with a slice or two of toasted French bread, and sprinkle generously with cheese.
Bake in an oven at 450 degrees or under the broiler until the cheese is bubbly and starting to get brown spots. Serve immediately.