In a food processor, coarsely chop mushrooms and lemon juice.
2 Melt butter in (4-5 quart) sauce pan and lightly sauté shallots on medium heat. Add mushrooms, thyme and bay leaf, sauté over moderate heat for 10-15 minutes, or until the liquid that is released from the mushrooms disappears.
3 Add salt, pepper, cream and chicken stock and bring to boil. Reduce heat and simmer for 20 minutes.
4 Add cornstarch and simmer for 10 minutes, stirring constantly. Correct seasoning and add more lemon juice to taste.
Serves 4. Serve sprinkled with a little parsley.