Slice the mushrooms and heat a large non-stick frying pan. Melt the butter and sauté the shallot (onion) until translucent (about 5 minutes). Add the mushrooms and toss about the pan until they are just cooked and wilted.
Add the garlic and cook for a further minute or 2. Add the sherry and wine and let this bubble until most of the liquid has evapourated then add the 2 tablespoons of flour and cook for a further minute or two. Transfer this to a medium pot and slowly add about a cup of the milk allowing it to be absorbed and soak into the flour. Then add the rest of add the milk and the stock. Season with salt and a generous few grounds of black pepper and about half the parsley. Let this bubble on the stock for about 30 minutes over low heat.
Process the soup with a stick blender or in a food processor/blender until smooth. Return to the heat and add the cream. This can be made in advance.
Serves with pan-fried sliced mushrooms, another drizzle of cream, and the rest of the chopped parsley.