Pork fillet is a really tender cut so great for quick-cook dishes like Mary's creamy stroganoff.
Remove any membrane from the pork fillet and discard. Cut into thin strips on the slant about 1cmx6cm ½in x 2½in. Season the meat with salt and pepper.
Heat a large non stick frying pan until hot, add a little oil when very hot and add the meat. Stir fry really briskly until brown, if cooked really fast there should be no juices, but take care not to overcook. Lift out with a slotted spoon onto a plate.
Measure butter to the pan, add sliced onions, cook over a low heat until the onions are really tender. Sprinkle in paprika, stir in the mushrooms, turn up the heat and toss for a minute, add meat to the pan with the cream, allow to just bubble to heat through, add lemon juice and seasoning and serve hot.
Serve at once, garnished with parsley with herby mashed potato and green salad.