The recipe I used was as follows (although see the comments at the end);
3 x lambs pluck boiled until cooked (half an hour or so)(came to 2.9kg in total but these were from very small lambs).
520g coarse oatmeal (note that that is oatmeal not porridge oats)
400g suet
5 tsp salt
1 tsp corriander
2 tsp pepper
1 tsp mace
1/2 tsp cayenne pepper
cut the tubes away from the pluck and discard.
mince the pluck
mix everything together
put in skins, vacuum bags or in a bowl with tinfoil on top that you can steam.
keep in fridge or freeze until needed.
reheat before serving by boiling/microwaving/steaming until it is properly hot through.
Next time I would tweak the seasoning a bit, probably an extra tsp of salt and definitely a bit more pepper and/or cayenne pepper - I think it should have a little bit of a kick to it but not too much. Given enough time you could probably play about with the spices quite a bit but the above is a good starting point.
I ran out of oatmeal and so substituted a bit of pearl barley - if you are going to do this cook it separately before mixing it in (I didn't think of this and have the odd hard bit).
Not sure if you are familiar with oats but just in case......porridge oats are rolled oats and are what most people make porridge with but people of my grandfathers generation wouldn't touch them (unless it was to feed horses). Oatmeal is ground (like in an old-fashioned water mill) and so has the appearance of crumbs of oats.
Ignore my previous comment about onion - I mis-remembered that!
Give it a go, I was surprised at how well it turned out - much better than the black pudding that I made which mostly ended up in the bin.
Tim