Directions

1. Bring a large pot of salted water to a boil. Add the pasta and cook according to package directions; drain (reserving 1/2 cup cooking liquid), rinse under cold water and drain again.
2. Heat 2 tablespoons of the oil in a large nonstick skillet over medium. Add the onions and cook until golden brown, about 15-16 minutes. Transfer to a bowl and reserve. Add the remaining oil to the skillet and stir in the shiitake mushrooms, white mushrooms, garlic, oregano and salt; cook until the mushrooms are browned and tender, about 16-18 minutes. Add the mustard greens and cook, stirring often, until the greens are wilted, 3-4 minutes. Stir in the onions, pasta and reserved cooking liquid and cook, tossing, until hot, about 2 minutes. Stir in the butter until melted. Remove from the heat and stir in 3/4 cup of the cheese, remaining 1/8 teaspoon salt and pepper. Divide among 4 bowls and sprinkle each with the remaining cheese.