This is more a wordy paragraph than a recipe, but what can you do with so few ingredients? The main principle is long slow cooking.Anyhow, you recall that my brisket recipe was the one My Sons (who have succeeded in burning water) managed to get ‘right’ even on the first try. For home, I buy the thickest piece of top rib roast I can find. It's usually cheaper than brisket, but also smaller. I usually buy about 2.5 - 3 lb to feed 6 (or to serve with chicken or turkey for a group of 12).
Lay roast (opened out flat) in a pan (like the doubled aluminum half steamer trays we used).
Slice a medium onion.
Mix ketchup 1:1 with water.
Add enough to totally submerge the roast.
Add a close fitting lid or a tightly wrapped double layer of foil.
Bake in a medium oven 300- 350° for at least 5 hours. Six hours at 300. More for a bigger roast. As long as the lid or foil is really tight you cannot overcook this. The meat should be 'falling apart' tender.
If you want to serve it with 'tzimmis':
Parboil yams (1 - 1.5 lb for a 3 lb roast) cut crosswise into 2 inch slices.
Peel when cool and add to the roast along with 1/2 lb each of dried apricots and plums.Either add yams and fruits during the last hour of cooking, or put them in the roasting pan before storing the roast overnight and then reheat with the fruits in the sauce. If you cook the fruits for the whole 5 hours they will fall apart.