It sounds just like corned beef, cooked with vegetables cabbage carrot potato onions, plus soaked dried peas cooked in a muslin bag.
The trick is to remove the salt
either by soaking overnight, and or say 3 changes of water
over an hour or two. I prefer to change the water
after having brought it to the boil for a while as this gets rid of some of the fat.
I add some mustard, a bay leaf and some peppercorns might help.
You simmer it for a couple of hours depending on size and add the vegetables part way through as they need less cooking
. it does seem to give a different flavour maybe as they get a bit of fat.
I don't know about the roasting idea. I doubt that it is a roasting meat. Maybe he just sealed it first. I have seen someone try to roast a pickled joint as it was called lamb? "ham" and the result could not be rescued.
There are also boil in the bag corned beef. I prefer also to get rid of all the gunk including the bag and after washing
change the water twice.
There are plenty of recipes
, but I think this covers the basics of what is involved.