Chop the onion into small cubes. In a soup pot over medium heat, melt lard and slowly brown the onion.
Clean and chop the oyster mushrooms. Add to the onions and sauté for a bit. Sprinkle with a teaspoon of cornstarch and deglaze with the soup.
Bring the soup to a boil and simmer for about 5 minutes, then finely puree with a hand blender, add salt and pepper and serve with voger lettuce leaves.