Wipe leg of mutton.
Bring sufficient water to cover leg to the boil in a large, heavy saucepan.
Plunge leg into water, add vegetables, bring to a slow boil and boil for 10 minutes before adding salt and pepper.
Cover, reduce heat and simmer for 2-2 1/2 hours or until meat is tender.
Skim off fat and leave leg in liquid whilst making Caper Sauce.
Serve boiled mutton surrounded with vegetables and accompanied with Caper Sauce.
To make Caper Sauce, melt butter in a saucepan, stir in flour, cook for 2 minutes over a medium heat.
Pour in hot liquid off the heat, stirring in a little at a time.
Return to heat, bring to the boil stirring continuously.
Season with salt and cayenne pepper and stir in capers.