Melt the butter in a saucepan and gently cook the mushrooms, peppercorns and parsley for 10 min. Add the flour and cook for a few minutes without browning it. Stir in the stock, bring the sauce to simmering point and simmer for 1 hr. Wring the sauce through a tammy cloth or damp muslin. Season, add lemon juice, and reheat. Just at boiling-point stir in the cream. The mushrooms may be rinsed and used as garnish for the dish.
Serve with chicken, veal, sweetbreads, fish or vegetables.