Heat the oil in a large non-stick frying pan. Add the lamb and brown on each side for 4-5 mins. Set the slow cooker to low. Melt the butter in a saucepan until foaming, then stir through the flour. Whisk in the stock gradually until incorporated, add the wine and bring to the boil. Set aside.
Put the onion, garlic, thyme and rosemary into your slow cooker and sit the lamb on top. Pour over the lamb gravy. Put the lid on and cook for 8 hrs or until soft and tender.
Remove the lamb and set, covered, on a plate. Strain the liquid into a pan and simmer until slightly thickened. Serve the lamb thickly sliced or shredded (it'll be quite soft) with mashed potatoes, green veg and the gravy.
Cook a leg of lamb in the slow cooker and be rewarded with tender meat that melts in the mouth. Enjoy with mashed potatoes and steamed veg.