In a large pot heat the oil over high heat. Season the beef with the salt and pepper and saute until browned. Remove the beef from the pot and set aside, pour off any excess fat in the pot.
Melt the clarified butter in the pot and saute the mushrooms and onions. Add the white wine and simmer until reduced by 1/2. Stir in the tomato paste and mustard and cook for 2 minutes. Add the demi-glace and beef, bring to a boil. Reduce the heat and simmer for 5 minutes. Stir in the sour cream and adjust the seasoning. Serve on a bed of warm egg noodles.
*Can be found in gourmet food stores