Marinade the meat for at least 12h in a mix of some random fat, random acid, salt, and seasoning. Then roast it in an oven bag. Slow and low heating (I use 125°C), trying to minimise the amount of vapour that is formed. It’ll take a few hours, and you need to flip it halfway so both sides get in contact with the juices. Near the end, if you want, open the bag and rev up the oven temperature, to brown it on the outside and, if there’s leftover juice, let it dry and coat the meat.

Which acid is up to you; I use alcohol vinegar if I don’t want it to interfere too much on the taste, otherwise I use a red dry wine for beef and lime juice for pork. The “random fat” is usually veg oil, just so the seasoning spreads more evenly across the meat.

Although… frankly, I’d rather use a pressure cooker for those.