Clean, clean and halve the mushrooms. Peel and finely chop the onion. Cut 2 slices of Parma ham into medium sized cubes. Cook the pasta in boiling salted water for about 8 minutes.
In the meantime heat oil in a pot and sauté the onion in it. Add Parma ham and mushrooms, sauté briefly and deglaze with vegetable stock. Add sour cream and bring to the boil. Stir in sauce thickener.
Season with salt and pepper. Drain the pasta and mix with the mushroom parma ham sauce and arrange on plates. Garnish as you like with the remaining Parma ham and oregano.