Peel and slice potatoes and onions and layer in a casserole dish, seasoning as you go, finishing with a layer
of potatoes on the top. Place a half shoulder of lamb on top, and season this also. Pour in enough stock
to come half way up the layers of veg, cover with a sheet of aluminium foil and roast in a 170°C oven
for about 90 minutes. Remove the foil and continue roasting for another 30 minutes, to brown the meat.
Carve into slices and serve accompanied with some green veggies.