Slice beef thinly across the grain.
Season beef lightly with salt.
Heat oil in a hot skillet.
Sear beef quickly until browned.
Remove beef and set aside.
Melt butter in the same skillet.
Add onions and cook until soft.
Add mushrooms and cook until golden.
Stir in garlic briefly.
Add mustard and paprika.
Pour in beef stock gently.
Simmer until slightly reduced.
Stir in cream slowly.
Return beef to the skillet.
Heat gently until coated.
Season with pepper and salt.
Garnish with fresh parsley.