Heat one tablespoon butter in a large frying pan and cook onion, mushrooms and garlic until softened-about 10 minutes.
Remove from the pan.
Toss the steak strips in flour which has been well seasoned with salt and pepper-I love heaps of pepper in this.
Add the remaining 2 tablespoons butter, heat and add the beef strips cooking quickly-about 2-3 minutes, until browned, but still a little pink inside.
Remove the meat and deglaze the pan with the wine, stock and tomato paste.
Add the paprika, mustard and pickles (these add a nice tart crunch to the sauce), then the sour cream. Mix well, add the mushrooms and meat back to the sauce, heat gently for a couple of minutes stirring all the time.