Buttery Black Truffle Mushroom Pasta

Name: Buttery Black Truffle Mushroom Pasta
Ingredients: 8 ounces uncooked linguine (reserving 1 cup pasta water); 1 tablespoon cooking oil ((I used rice bran oil)); 2 tablespoons unsalted butter; 1/2 medium yellow onion (diced); 8 ounces cremini mushrooms (sliced); 8 ounces King oyster mushroom (diced); 1 tablespoon flour; 3 tablespoons black truffles in oil ((I use Urbani Truffles)); 1/2 cup parmesan cheese (grated); 1/4 teaspoon kosher salt; fresh cracked black peppercorn ((to taste)); 1/4 cup parsley leaves (chopped)