Preheat oven to 325ºF (170ºC). Thoroughly dry the ribs with a paper towel then season the short ribs on both sides with salt and pepper.
Heat a Dutch oven over medium heat, add the oil and heat through. In batches to avoid over-crowding the pot, add the short ribs to the pot and sear until they are browned on all sides, about 6 minutes. Remove to a plate and set aside. Continue with the remaining short ribs and set aside.
In the Dutch oven over medium heat add the onion, carrot, celery and garlic, sautéing until the vegetables are tender, about 5 minutes. Add the flour and stir constantly, letting cook until the flour turns light brown, about 3 minutes.
Add the tomato paste and stir to combine before adding the red wine, beef stock, rosemary, bay leaf and short ribs to the pot. The ribs should not be completely covered by the liquid. Bring the mixture to a boil over medium heat then cover the pot and place in the oven.
Cook, rotating the short ribs about every 45 minutes, until the meat is fork tender, about 2½ hours, removing the lid for the last 30 minutes of cooking. Remove from oven and let sit for at least 5 minutes then skim off any fat from the top and discard.