Take a leg of lamb with bone Wash under running cold water and pat dry. Season with salt and pepper. you can also use Aromat (flavour enhancer), Season-All, garlic and coriander.
Quarter an onion and put in a roasting pan with the meat. It's good to rub the meat with the onion before seasoning.
Cover and insert into a heated oven (175-200° C.).
Allow the meat to brown on the outside, about 15-20 minutes.
Pour in some water to cover the bottom of the pan, and add more water as it evaporates.
Baste the meat with the water and juices. The roast should stay in the oven for about 2 hours. After about 1 1/2 hours, take the roast out and pour off the cooking liquid. Return to the oven without covering, to brown. Use the cooking liquid to make the sauce (see recipe below).
Alternate method: If you have enough time, slow-roast the meat. Treat as above, cover and insert into a 200°C oven. Lower heat immediately to about 125°C Allow to brown and add water.
Slow roast at 125°C for 1 hour, then turn up the heat to 150°C and roast for another hour.
Turn up the heat to 175°C and roast for a third hour. Pour off the liquid and put uncovered into a 200°C oven to brown. Icelandic lamb is very tender, and this slow cooking method makes it so soft that it almost melts off the bone, while still retaining the flavour.
Sauce to serve with Sunday roast: Pour the cooking liquid off the meat through a strainer. Put the onions in the strainer and mash into the liquid. Skim off the fat. Heat to boiling. Mix together some water and flour into a smooth, thin paste. When the liquid boils, add the flour paste, stirring constantly, until sauce begins to thicken. Stir well to mix. Strain if the sauce is lumpy (sift the flour to avoid this). Heat to boiling again, and add some cream (not strictly necessary, but improves the flavour and smoothness). Adjust the flavour with salt/spices if necessary.
For an authentic Icelandic Sunday roast, serve with the sauce on the side, boiled or caramelized potatoes, green peas and rhubarb jam. For my part, I like to leave out the peas and jam and serve instead a fresh salad and some sautéed mushrooms. If you feel like eating anything else after this heavy repast, ice-cream is the favoured dessert. Home-made ice-cream is especially good.