Remove excess fat from meat, but not too much as you still want the meat to be tender and tasty. If while you're cutting the fatty layer between the rack of ribs and the flap of meat the two come apart, don't worry, just brown the flap of meat and then brown the ribs separately. In fact, I sometimes separate the two on purpose and then cook them, low and slow, together afterwards.
Brown meat (meaty side down) with a little oil in large frying pan.
Once the meat is brown, remove from pan and set aside either in an ovenproof dish or your crockpot/slow cooker.
To the same pan in which the meat was browned, add all the onions, carrots and celery and continue to fry over medium to high heat until onions are limp.
Add sugar, red wine, beef stock and thyme and continue to cook.
Once boiling, reduce heat and allow to simmer for 4 or 5 minutes.
Spoon the vegetables over the meat and allow to cook in the oven 300 Deg F(140 Deg C) tightly covered with tinfoil for about 6 - 7 hours. Check halfway through to see that there is enough liquid. If it's starting to dry out, add beef stock (1 bouillon cube to 1 1/2 cups boiling water). If it's in your crockpot, on low, it probably won't need more liquid and can cook for about 8 - 9 hours.
You can either add potatoes to the dish (pushing them down and around the meat) or serve with potato kugel or creamy mashed potatoes. Remember the potatoes cooking with the meat will absorb some of the liquid.