Cooking the roast
Preheat oven to 135°C (275°F).
Mix rub ingredients together, and rub over meat.
Put meat fat-side down in an oven-safe dish, covered (I use the large ceramic dish from our slow-cooker and cover it with aluminum foil).
Cook in oven for 4 hours and then flip fat-side up and cook for 1 hour.
Remove from oven.
Preparing the sauce
On the stove-top, place onion and juices from roast in a sauce pan on medium-high heat.
Once the juice starts boil off (before the onions burn), add vinegar and brown sugar.
Continue boiling off steam until the mixture is reduced to a syrup.
Brush about half of the sauce on the roast, and place it back in the oven, uncovered.
Broil until top is lightly browned. 3