French Onion Soup with Cheese Croûtons

Properly made, which means long, slow sweating of the onions, French onion soup is the most comforting winter food in the world. Last time we had it, it was the main course for lunch after a long, chilly walk with friends.

Ideally, you would have time to make your own rich stock by roasting veal and beef bones in the oven until brown, then putting them, with any juices and bits from the roasting tin, into a big saucepan with water, fresh herbs, a large onion and a couple of carrots,