Heat the oil in a large (11-12-inch) Dutch oven or heavy-bottomed stockpot over medium heat. Add the pancetta and cook for 4-5 minutes, until browned. With a slotted spoon, transfer the pancetta to a plate lined with a paper towel and set aside.
Meanwhile, season the short ribs all over with 2 teaspoons of sea salt and 1 teaspoon of black pepper. Brown half the meat in the pot over medium heat, turning occasionally, for 5-7 minutes, until browned on all sides. Transfer the meat to a bowl and brown the second batch. Transfer the second batch to a bowl and set aside.
Off the heat, add the cognac and 1/3 cup red wine to the pot, scraping up any browned bits, then simmer over medium heat for one minute. Add the onions and fennel and sauté, stirring occasionally, for 7 to 8 minutes, until the vegetables are tender. Add the garlic and cook for one minute.
Stir the tomatoes and tomato paste into the vegetables. Add the remaining 2/3 cup of wine, the beef broth, the seared meat and juices, 2 teaspoons sea salt, and 1 teaspoon black pepper. Bring to a simmer, cover, and bake for 1 1/4 hours, checking occasionally to be sure the liquid is simmering. Degrease the stew, if necessary. Stir in the carrots and potatoes, cover, and bake for one hour longer, until the vegetables and meat are very tender when tested with a fork. Just before serving, stir in the peas and pancetta, taste for seasoning, and serve hot in large, shallow bowls.
*If you want to make it ahead of time, simply reheat it over medium-low heat, adding beef broth and a splash of red wine as needed.