1 1/2 lb. well trimmed beef tenderloin
Salt and pepper, to taste
8 tbsp. butter
4 tbsp. vegetable oil
1 lb. onion, thinly sliced
1 lb. mushrooms, thinly sliced
2 1/2 tsp. dry mustard
1 tsp. sugar
2 1/2 c. sour cream
Finely chopped parsley

1. Cut meat into 1/2" thick slices, then cut each slice into strips about 2 " long and 1/4" wide. Season with salt and pepper. Set aside.

2. In large skillet, heat 4 tablespoons butter and 4 tablespoons oil together over medium low heat and saute onion until softened.

3. Raise heat and add mushrooms. Cook until tender and liquid has evaporated. Set aside.

4. In a cup, mix the mustard and sugar with just enough water to make a paste. Set aside.

5. In another skillet, melt the remaining 4 tablespoons butter over medium high heat and quickly saute the beef strips. Do not over cook.

6. Add the cooked beef to the mushrooms, then stir in mustard paste, then sour cream. Correct seasoning and place over medium heat. Bring to boiling point - but do not boil. Sprinkle with parsley and serve immediately over noodles.