3 bay leaves
minced garlic to taste (I like a lot)
1/2 tsp salt
1/4 tsp cloves (or so, I just lightly sprinkled it on)
1/3 to 1/2 cup apple cider vinegar
Trim the fat from the roast. Slice or quarter the onion (your choice - I like slices). Put the meat and onion in the slow cooker; add bay leaves, garlic, salt and cloves. Pour apple cider vinegar over it and cook on high for about 5 hours (obviously, cook it until it's done). For low, probably 11 hours.
The meat came out incredibly moist and the apple cider vinegar added a great flavor to both the meat and the onion. I served it with brown rice and green peas. You could probably use a beef roast too. If you want the juices (either for gravy or on the side) you'll want to strain/skim the fat and garlic bits and stuff out.
As I understand it, if you cook it longer, you end up with meat that's shreddable and good for bbq-style shredded meat sandwiches. Even at 5 hours, it was really tender.