Pre-heat your oven to 325F.
Heat a big dutch oven over medium heat. Add enough oil to generously film the pan.
Working in batches, deeply brown the beef on all sides. Take your time. You are going to spend 15-20 minutes on this. It is THE critical step. This is where the depth of flavour comes from. This is magic.
Once you have finished browning the meat spoon out all but about 4 Tbsp of fat from the pan. Add the pancetta and cook until golden - about 2 minutes.
Reduce heat to medium low and add the onion, leek, and carrot. Cook, stirring occasionally, for about 10 minutes. Add the garlic and tomato paste. Cook 2 minutes more, stirring constantly.
Add the wine. Bring to a boil and let simmer 5-10 minutes.
Return the beef to the pot along with 4 cups veal or chicken stock.
Make a bouquet garni and nestle it in with the beef.
Cover the pot with a sheet of aluminum foil and then the lid. This creates a better seal and makes cleaning up easier.
Place the dutch oven in the oven. Check for doneness after about 2 hours. You are going for fork tender. If it's not ready put it in and cook another 30 minutes. Check again. If it's still not fork tender then let it go another 15-20 minutes. It will be done by the 3 hour mark.
Remove the dutch oven from the oven and remove the meat and bouquet garni. Discard the bouquet garni and tent the beef with foil.
Strain the sauce, pressing down hard on the onion/leek/carrot mixture to extract all the liquid. If you can force a bit of the vegetable pulp through the strainer that's good too. It adds a little something but it's not critical.
Return the strained sauce to the pot and simmer to reduce by half. This takes about 20-30 minutes.
Return beef to pot and simmer to warm the beef through.
Serve braised short ribs and sauce with crusty bread. Or serve it on spätzle or tagliatelle.