Purée of Onion Soup with Thyme Leaves*

• 45 g/1½ ozs/3 level tablesp. butter
• 450

Peel and chop the onions and potatoes into small dice. Measure. Melt the butter in a heavy saucepan. As soon as it foams, add the onions and potatoes; stir until they are well coated with butter. Add the thyme leaves, season with salt and freshly-ground pepper, cover with a paper lid (to keep in the steam) and the saucepan lid, and sweat on a low heat for 10 minutes approx. The potatoes and oni