Roast mustard & rosemary Lamb

Season a 2 kg lamb leg and make deep cuts all over the meat. mix 1 tbls french grain mustard with a sprig of finely chopped rosemary the juice of 1/2 lemon and smear over the lamb. Slice 2 onions and sprinkle over the bottom of a roasting tin. sit the lamb on top drizzle with olive oil slosh in 250ml sparkling white wine (or Prosecco) 150ml good chicken stock 2 bay leaves and a halved bulb of garlic and roast for 30 mins in a hot oven 220c- then turn the oven down to 170c cover the lamb in foil and roast for another 2.5-3.5hrs until the meat is tender and falling from the bone. to make the gravy, skim off most of the fat, strain liquid into a saucepan with a little more wine, add a little more stock or some water from your drained vegetables, mix a little flour with water & whisk this in over the heat til thickened season to taste and serve with your lamb