You can use either sausage meat or deskinned sausages that already have herbs in & add say, finely chopped onion, fresh or dried herbs, chestnuts (roasted 1st for 1/4 hr, then skinned & simmered in a little milk for about 3 minutes mashing them. The gammon will need to be soaked in water for 12 to 24 hrs then drained to make it less salty - unless it`s a "sweet" or mild cure one. Boiling takes 30 mins a lb plus 20 mins, even big ones should be done in 31/2 hrs. You can leave it in the water to cool overnight & skin it next day when you can coat it with breadcrumbs or brown sugar & stick cloves in it then about 10 mins in a hot oven. Many recipes state cloves in the water, & some beer,or cider or red wine.