Heat oil in pan over high heat. Cook mushrooms, for 4 minutes, stirring occasionally until light golden. Add the onion, garlic and mince, cook, stirring to break up mince for 5 minutes until beef is browned.
Stir in paprika, tomato paste, Worcestershire sauce and mustard. Season with sea salt and freshly ground pepper. Add pasta and stock to pan. Bring to the boil, reduce heat to medium-low, cover and cook for 10 minutes, stirring occasionally to prevent pasta sticking to bottom of pan.
Meanwhile, finely chop chives and half the parsley, pick the remaining parsley leaves. Stir sour cream and chopped parsley into pasta and cook, uncovered for 2 minutes or until pasta is al dente. Season. Serve scattered with chives and parsley leaves.
