Preheat oven to 220C. Remove leg of lamb from the fridge about 30 minutes before cooking
Using a deep roasting tray, line the tray with sliced onions
Make a number of incisions into the lamb approx. 3cm deep using a sharp knife. All over the surface of the leg of lamb
Using a longer, sharp knife, make a few deeper incisions into the thicker parts of the leg approx 10cm deep
Into each of the smaller incisions, insert a sprig or two of rosemary, slither of garlic and anchovies each. Repeat all over the leg.
In a small bowl, mix together the finely chopped garlic, anchovies, rosemary (dried if using) and capers, ready for use
Into each of the deeper incisions, spread the finely chopped stuffing throughout the leg
Place the prepared leg of lamb on top of the bed of onions
Drizzle the oil from the anchovies onto the leg of lamb
Roast the leg of lamb for 20 minutes at 220C
Turn the temperature down to 180C and add the water to the roasting tray. Cook for the remaining time at 25 minutes/500g.
Remove lamb from the roasting tin and rest on a pre-heated baking tray for 15-20 minutes.
Whilst resting, prepare the gravy by pouring all the juices from the roasting tin into a saucepan. Add the flour and red wine and bring to the boil whilst constantly stirring. Add more water to volumise the gravy. Adjust taste with salt and pepper then keep warm on a low heat.
Carve the lamb and serve with roast potatoes and vegetables of choice.