1. Soak mushrooms in warm water for about 30 minutes. 2 .Peel potatoes and cut roughly into cubes. 3 .In a pot, saute chopped onions in butter over high heat. Add the potato cubes and saute for about 3 - 4 minutes.4 .Pour in the stock, bring to a boil, then simmer over medium heat for about 20 minutes. 5 .Drain mushrooms and wash under running water. Cut into thin slices. 6. Transfer the potato soup into a food processor. Puree, then stir in the cream, sliced mushrooms, and marjoram. Season with salt and pepper. 7 .Reheat in the pot for a few minutes. Serve with warm toasts