Everyone asks me about this recipe! Fast and tasty! Easy pasta and beef recipe!

INGREDIENTS:
700 g beef rump (1.5 pounds)
1 onion
olive oil
2 tbsp butter
2 tsp salt
pepper
200 g mushrooms (7 oz)
1 tbsp Dijon mustard
400 ml beef broth (1 2/3 cups)
1 tbsp flour
3 tbsp 30% sour cream

Garnish:
Noodles