Combine the sherry and garlic in a mixing bowl. Add the lamb cubes and baste well. Cover and set aside to marinate at room temperature for 3 hours, basting occasionally. Remove the cubes from the marinade and pat dry with kitchen towels. Reserve the marinade.

Rub the cubes with salt and pepper to taste, then the cumin.

Heat the oil in a large saucepan. Add the lamb and fry until it is evenly browned.

Add the onions and fry until they are soft. Stir in the flour until it is well blended, then pour over the reserved marinade, stirring constantly.

Bring to the boil. (If the sauce is too thick, add a little water.) Reduce the heat to low, cover the pan and simmer the stew for 1 to 1 1/4 hours, or until the lamb is cooked through and tender. Remove from the heat and serve at once.