Porcini Mushrooms and Potato Soup

Ingredients

• porcini mushrooms - 1.1 oz (30 g) dried
• warm water - 10 fl oz (300 ml) for the mushrooms
• butter - 0.7 oz (20 g)
• onions - 1 onion
• salt - to taste
• black pepper - to taste
• garlic - 2 cloves
• field mushrooms - 10.5 oz (300 g)
• oregano - as needed
• potatoes - 1 - 2
• mustard - 1 tsp.
• worcestershire sauce - 2 tbsp.
• beef broth - 2 cups (500 ml)
• white wine - 3 tbsp.
• sour cream - 3.4 fl oz (100 ml)
• water - 2 cups (500 ml) for the soup
• prosciutto - for serving