Remains of the Sunday roast, seperate the fat out and put it into a big pot. Peel and dice an onion and fry it in the beef fat until golden.....if you don't have fat just use butter.
Scrape out the roasting tin and shred the bits of meat off the bone if there is one or break up the end of the plain roast. Rinse out the last of the jus from the roasting tin too and add that to the pan as stock.
If you have left over veggies from S.L. you can use them up, otherwise scrape and chop up a couple of the big Winter carrots, do the same with a couple of big spuds.....biggish chunks.
If there's not a lot of meat add some link sausages to the pot too.
If you don't have meat, then an old Irish neighbour used to just open a can of corned beef and make hers with that.
Season generously with ground pepper and some salt. Cook long and slow until the spuds are cooked and the carrots have gone sweet.
If you like doughballs, (dumplings ?) then make sure there's enough gravy in the pot for them to rise. The extra flour on them will help to thicken the gravy too. Really good with herby or cheesy doughballs.
Scots call this dish Stovies.
If you do it in the oven then you can make some cheese scones and place them around the marmite pot rim to cook crisp on top and soft underneath.
The Vegetarian version uses the same onion, and a couple of cloves of garlic, fried up in whatever oil or fat one chooses. Season that oil towards the end with herbs and celery salt. Add veggie stock of choice (Marigold or Vecon), a handful of quick cook peas or lentils, and mostly cook the veggies. Instead of meat add big chunks of mushroom or marinaded or braised tofu, or pre-made veggie bangers cut into chunks, but do it towards the end of cooking so they're soft but not tasteless.
It's very good
p.s. Marmite pot (pronounced Marmeet) is the big heavy cauldron shaped crockpot that is used to cook beans and the like in the oven. A big casserole dish works just as well, and a Dutch oven is very good for it too.