Slice tenderloin across the grain into 1/4-inch pieces. Salt and pepper both sides of the sliced rounds of pork.
Heat half of the oil and butter in a large frying pan. Fry the pork in batches about 3 minutes per side until brown. Remove the pork to a plate and cook the next batch.
Add the rest of the butter and olive oil to the pan. Add the onions and season with a little salt and lots of black pepper and cook until they are soft, they don't need to be brown, just soft. Add the mushrooms. Stir them until they begin to soften and exude their juices.. Season with salt and black pepper. Remove onions and mushrooms to another plate or bowl.
Return the pork and any accumulated juices to the pan. Move the pan to a burner that is not heated and add the gin. Move it back over to the heat and allow it to warm for a minute. Using a long lighter, set fire to the gin and baste the pork until the flames go out.
Return the onions and mushrooms to the pan stir in the sour cream and bring it to a bubbling simmer for a few minutes.
Just before serving stir in the paprika.
Served on cooked egg noodles and sprinkle with parsley.