Roquefort comes from the Auvergne, a region of France that British people have a particular affection for. It is a very rich cheese with a strong, spicy taste. This simple salad is one of the best ways to appreciate its flavour. Make sure the cheese is well chilled before use, so you can crumble it easily. Choose the walnuts and walnut oil carefully; if old, they will taste rancid and unpleasant. Should you wish, you can replace the chicory with any other salad leaves.