Melt Butter. Add onions, salt and pepper. Saut=E9 10 minutes, add stock and bring to a boil. Cover and simmer for 10 minutes. Add half the mushrooms and let soak for 1 minute. Puree in blender/food processor until smooth. Add 15% cream and heat gently. Drop in remaining mushrooms and cook slowly until tender. Serve with a dollop of whipped cream and a dash of cayenne (or paprika) for color. Use a warmed bowl (of course).