Cut the meat into portions and fry them until reddened in the butter. Take them out with a slotted spoon and braise the flour in the same butter.
Leave it to boil on low heat. Chop the leeks into 2 1/2″ (6 cm) long pieces.
Boil them in lightly salted water and add them to the meat, while leaving it to boil a bit more. Serve with slices of lemon.