Preheat oven to 350º. Generously season flour with salt and pepper, and dredge each short rib in the flour mixture.
In a dutch oven, cook pancetta or bacon over medium-high heat until crispy, remove from the pan and save for another recipe or salad, but leave behind the fat for cooking.
Add olive oil to pan and add short ribs, browning them on all sides, about 1 - 2 minutes per side. Remember this tip: you can't braise if you don't brown! Remove short ribs and set aside.
Add onion and shallots to the pan and cook until softened, about 3 minutes.
Increase heat to high and stir in wine and deglaze the pan (a.k.a. scrape up all of the cooked on goodness at the bottom of the pan!)
Add short ribs back in and bring to a boil.
Lower heat to medium and simmer until wine is reduced by half, about 25 minutes. The sauce will be thick and bubbly.
Add garlic, rosemary sprigs and bay leaves to the pot and add enough beef stock to cover short ribs.
Return to boil, then cover and move to oven.
Cook for 2 - 2 ½ hours until short ribs are fork tender and pretty much falling off of the bone.
Just before serving, spoon fat from surface of sauce and discard. Top short ribs with Chianti sauce.