In a large pan with a heavy base, sauté sliced onions VERY slowly on a LOW heat. The pan will be overflowing initially, but the onions will slowly cook down to a fraction of the volume. This slow cooking process can take an hour or more. Stir every 10– 15 minutes until the onions are caramelized and golden.
While the onions are cooking, toast the sliced baguette. Shred the cheese. Set both aside.
Once the onions are golden and completely reduced down, add the Madeira to loosen all the caramelized bits of onion at the bottom of the pan. That’s where a lot of the flavour is. Cook off the alcohol on high for a few minutes, then add the stock and heat the soup through.
Turn the oven on broil. Ladle the onion soup into oven proof bowls, top with sliced toasted baguette and sprinkle generously with cheese. Broil for a few minutes (watch carefully because it burns easily). Once the cheese is melted, remove and serve immediately!
Note: Even though I’m a self declared saltoholic, I don’t add salt to this recipe. The cheese is salty enough.