Preheat the oven to 350°F (180°C) mark 4.

Trim and wipe the mushrooms and slice thinly. Sweat the shallot in the butter with the sprig of thyme for 5 minutes, increase the heat, add the mushrooms with a pinch of salt and saute for 2 - 3 minutes.

Add the stock, cover and simmer gently for 15 minutes (reduce this to about 5 8 minutes if using field or cultivated button mushrooms). When the mushrooms are very tender, add a little more salt if wished and plenty of freshly ground white or black pepper, remove the thyme and push the mushrooms through a fine sieve, collecting the puree in a bowl (or use a food processor). Blend in the cream and milk.

Separate 2 of the eggs and beat their yolks lightly with the remaining 2 whole eggs, a pinch of salt and pepper and the Parmesan cheese. Blend into the mushroom mixture.

Grease four 7 fl oz (200 ml) capacity timbale moulds or ramekin dishes with butter. Fill them with the mushroom mixture, place well spaced out in a roasting tin or similar receptacle and pour in enough boiling water straight from the kettle to come about half to two thirds of the way up the sides of the moulds. Cook in the oven for 30 minutes; their contents will gradually thicken and set in a firm custard mixture.

Make the sauce while the moulds are cooking. When they are done, turn off the oven and leave them inside for 10 minutes, still in their bain marie with the door ajar. Unmould on to heated individual plates and serve with the sauce.