Keep aside 4-5 mushrooms. Slice them finely and stir fry them with salt and pepper till it becomes golden brown n crispy.
In a food processor, coarsely chop rest of the mushrooms and lemon juice.
Melt butter in (4-5 quart) sauce pan and lightly sauté sliced 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.
Add salt, pepper, cream and chicken stock and bring to boil. Reduce heat and simmer for 20 minutes. Add white sauce (if using) and cook for another 5-7 mins. Add more salt and pepper if required and remove from fire.
Add chopped fresh parsley and garnish with stir fried mushrooms.
To make white sauce:
Melt butter in a deep sauce pan and add flour. Roast it till the raw smell goes, 3-5 mins, on low flame. Add the whipping cream gradually and mix well. If it becomes too thick, add little milk to loosen it. It should have a pouring consistency.