Unwrap the gammon, leaving the strings and paper on, and place in a large pot with the onion.
Cover gammon with lemonade and boil for 1 hour and 50 mins, keeping the lemonade topped up. (For other gammon weights do the following: 850g boil for 45 mins or bake for 20 mins, 2kg boil for 1h 20 mins or bake for 30 mins.)
Put the apricot jam and ground ginger into a saucepan and mix together over a medium heat. Set aside until gammon has boiled.
Place the boiled gammon in a casserole dish, removing the string, paper and rind.
Score, then stud the gammon with whole cloves.
Thickly spoon on the glaze, spreading it over the top of the studded gammon. Add the muscovado sugar on top of the glaze.
Bake in a pre-heated oven at 185ºC, or Gas Mark 4, for 30 mins.