Start with 3 or 4 large onions, preferably of the sweet variety. Other types will do, but the sweet ones are my favorites to work with. Slice them thinly, and toss them into a soup pot with some melted butter and olive oil. Why both oil and butter? The butter adds flavor, and the olive oil stops the butter from burning. Next, add a bit of salt, some sprigs of fresh thyme, two or three crushed garlic cloves, and a splash of water, and turn up the heat.
Starting with high heat and a little extra water will help drive the moisture out of the onions. This is the first step to getting them to that beautiful golden brown color that you are aiming for. Until the water is mostly gone you won’t be able to get to the temperature you need to start the camelization process, because evaporation cools them down too much. However, once the onions are reduced in size and there isn’t much liquid around them, you will need to turn down the heat to prevent them from burning. This is really the only tricky part to making French onion soup, and it is better to err on the side of caution and keep the heat low. That way the only bad thing that happens is that it takes longer to cook the onions.
After the onions reach the desired color (darker is sweeter), you will need to deglaze them. This just means adding a liquid to the pot and then scraping off the cooked bits from the bottom of the pot. White wine is the best for this recipe, and what I do is toss a quarter cup of it in and use a wooden spoon to get the dark bits off the bottom. After the wine has been absorbed or evaporated, I repeat the process three times. This infuses a lot of flavor into the onions.
After the deglazing, add the remaining ingredients. First, stir in a tablespoon or so of Dijon mustard, then add in another half cup of white wine. Last, add 2 quarts of beef stock, or if you want a lighter taste add one quart each of beef and chicken stock. Bring the soup up to a simmer and leave it there for about 15 minutes.
If you want to stop at this point, you will have a wonderful soup just the way it is. But if you want to go all-out you can add the baked cheese topping without too much trouble. First, slice some nice French bread (we may as well stay on theme, right?), and some Gruyere cheese. You can use Swiss cheese instead if you like, but Gruyere is the classic choice. When the soup is done simmering, ladle it into oven-proof onion soup bowls that are sitting on a baking sheet. Add a slice of bread to each bowl and top with some cheese. Put everything under the broiler for a minute or so until the cheese is melted and is just starting to get brown on the edges. Be careful! Burning yourself on one of the bowls would be bad enough, but pouring piping hot soup down your front is altogether unpleasant.
Serve the soup with some extra slices of bread. Make sure to put the bowl and the bread on a plate to prevent burns to either fingers or place mats.
Here are the ingredients listed again for convenience:
3 or 4 large onions;
2 or 3 cloves of garlic;
butter and olive oil;
a bit of water (maybe a quarter cup);
sprigs of fresh thyme;
cup and a half of white wine;
2 tablespoons of Dijon mustard;
2 quarts of beef stock, or 1 quart each of beef and chicken stock;
French bread and Gruyere cheese (optional)