Make a more sophisticated sauce by replacing half the stock with either red or white wine.
Coat the pork: Cut the pork diagonally into finger-thick slices. Tip the flour and rosemary into a large plastic food bag, add some salt and pepper and the pork, and toss until the meat is well coated.
Start cooking: Heat 2 tablespoons of the oil in a large wide frying pan. Add the pork and fry for about 3-4 minutes until nicely browned on both sides, turning once. Remove from the pan.
Fry the mushrooms: Heat the remaining oil in the pan, tip in the mushrooms and fry until they start to soften, about 2 minutes. Sprinkle in the garlic and return the pork to the pan with any flour left in the bag. Stir in the stock and bring to the boil. Simmer for 5 minutes or until the pork is cooked.