Season beef strips with a little salt and pepper. Heat a large skillet or sauce pot over medium-high heat. Add oil to pan and sear beef on all sides to medium rare, approx. 2 min. Remove beef from pan and set aside, reserving all juices. Sear wild mushrooms in same pan, adding more oil if needed. Remove mushrooms from pan, adding them to the beef. Add to the hot pan: butter, shallot and garlic, cooking until fragrant and softened, approx. 2 min. Add flour, cooking until golden, approx. 1 min. Add sherry and reduce by half. Add mustard, seasonings, sauces and stock and bring to a simmer. Add sour cream and parsley and return to a low simmer, whisking until smooth. Add reserved beef and mushrooms with all juices and heat through. Toss with warm, cooked pasta and serve immediately garnished with fresh parsley.