Preheat 1/2 cup of olive oil on the stove and add the brown sugar. Stir and pour in the tomato puree, mustard and wine. Simmer until the liquid evaporates and stir evenly. Coat the leg of lamb on all sides evenly with this mixture.
Bake it in a greased tray, in which you have added about a cup of hot water, cover it carefully with foil, preheat the oven to 392°F (200 °C).
Bake for about 1 1/2 hours, then remove the foil and roast to a delicious crust.