Pat the short ribs dry and season with salt and pepper.
Coat a large, nonstick pan with olive oil. Sauté the short rib pieces over medium-high heat for about two to three minutes on each side or until brown. When finished, transfer the short ribs to a bowl.
Next, add the onions to the pan and cook over medium heat for approximately three minutes. Once the onions are translucent, add the garlic and cook for one minute.
Add the Chianti, rosemary, beef broth and tomatoes to the pan one at a time, allowing the liquid to evaporate partially before each addition (about two minutes).
Return the short ribs to the pan, including any juices that might have accumulated in the bowl. Cover and let simmer for three hours on low heat to complete the braising process.
Remove the short ribs from the pan and boil the liquid until it’s reduced by half, about 10 minutes.
Return the short ribs to the pan and heat thoroughly.