For sunday roast brisket.
I fry the joint to seal it, then chuck in an onion chopped in half, 2 carrots, a bouquet garni, about half a bottle of red wine and some swiss vegetable bouillon. Transfer it all to the crock pot, put a lid on it and stick ot on gas mark 3 or 4 for 2 and half to 3 hours.
Its all guess work. Cook it slow and on a low heat. If you then take the joint out to rest, pull the bouquet garni out and blitz the gravy, reduce it on the stove whilst you dish your other stuff up.
My mum alternatively, boils it a bit and then roast it like normal and hers is tender too. Im just a pot roast fan.