- 2 tablespoons butter
- 2 tablespoons olive oil
- 2 large yellow onions, coarsely chopped
- 1/2 pound brown or white button mushrooms, sliced 1/4-inch-thick
- 1/2 pound wild mushrooms, sliced 1/4-inch-thick
- 1 large russet potato, peeled and coarsely chopped
- 1 tablespoon chopped Italian parsley, plus additional for garnish
- 2 teaspoons coarse salt
- Freshly ground black pepper, to taste
- 4 cups vegetable or chicken stock
- 1/2 cup cream or crème fraîche
- 2 teaspoons Worcestershire sauce
- 1/2 cup finely grated aged Pecorino cheese
In a heavy-bottomed stockpot or Dutch oven, heat butter and olive oil over moderate heat. Add onions and cook, stirring occasionally, until onions are light golden brown and translucent, 10 to 15 minutes.
Add mushrooms and cook, stirring occasionally, until mushrooms have released their juices and start to turn golden brown at their edges. Add potatoes, parsley, salt and pepper. Cook for about 5 minutes more to meld the flavors.
Add stock and bring the soup to a boil. Lower the heat and simmer, partially covered, until potatoes are tender, 25 to 30 minutes.
Transfer soup to a blender or food processor and blend in batches until smooth (use caution when blending hot soup and be sure not to fill the blender more than half full). Return the soup to the pot, stir in cream and Worcestershire sauce. Adjust seasonings. Stir in half of the cheese just before serving.
Serve hot soup garnished with remaining cheese and chopped parsley.