Melt butter in a heated pan. Saute chopped shallots and then add mushroom slices. Add lemon juice, black pepper powder, bay leaves, and vegetable stock. Prepare a slurry using corn starch and water. When the vegetable stock boils add the corn starch slurry to it. Stir well and when the soup thickens, turn off the gas and allow the soup to cool at the room temperature. Blend the soup well and strain. Pour the strained soup again in a heated pan. Mix some cream. Season again with black pepper powder and salt. Stir well. Add some chopped mushrooms and onions. Transfer the hot soup to a bowl. Take some soy sauce in a soup spoon and place it in the serving dish. Garnish the soup with coriander and a mushroom slice and serve the soup hot.