Special equipment: a pressure cooker (see Cook's Note)
Season the short ribs with 1 teaspoon each of the salt and black pepper. Heat the oil in a pressure cooker over medium-high heat. When hot, add the short ribs and sear on all sides, 4 to 6 minutes. Remove from the pressure cooker and reserve.
Lower the heat to medium, add the onions, carrots, celery, garlic, sage and thyme and cook until lightly caramelized, 6 to 8 minutes. There should be a fond-- tasty bits from searing the ribs--on the bottom of the pan. Add the red wine and chicken stock and, using a wooden spoon, scrape the bottom of the pressure cooker to get the fond into the sauce. Let the wine reduce for 6 minutes. Add the short ribs back to the pressure cooker and stir well. Add the pressure cooker lid, line up the arrows and, following the manufacturer's instructions, keep over medium heat while the cooker pressurizes. Cook over medium heat until the ribs are tender and almost falling off the bone, 45 minutes. Remove the pressure cooker from the heat and carefully release the steam through the pressure valve on the lid, following the manufacturer's instructions. Transfer the ribs to a plate. Reserve to the side.
Strain the cooking liquid from the pressure cooker into a small saucepan and cook over medium-high heat until reduced by half, about 15 minutes.
Meanwhile, in a separate saute pan, combine the red wine vinegar, barbecue sauce, brown sugar, hot sauce, red pepper flakes, remaining teaspoons each of salt and black pepper and whisk together well. Bring the sauce to a simmer. Add 1 cup of the reduced cooking liquid to the barbecue sauce mixture and cook until thickened, another 5 minutes.
Prepare a grill for medium-high heat. Place the short ribs on the grill, baste with the barbecue sauce, and cook until they have started to caramelize, 2 to 3 minutes. Baste the short ribs with the sauce, flip the ribs, and cook until the other sides start to caramelize, 2 to 3 minutes more. Remove the short ribs to a cutting board and allow to rest 5 minutes.
Serve the BBQ short ribs over a bed of Roasted Red Pepper Polenta; drizzle with more barbecue sauce and garnish with sliced scallions, if using. Serve immediately.
To fire-roast the red peppers, place them over a high flame on a stove-top burner and roast, turning occasionally, until the skins turn black on all sides. Place the peppers in a medium bowl, cover with plastic wrap and allow them to steam for 10 minutes. Peel away the blackened skins from the peppers. Cut away the stems and then seed, core and coarsely chop the peppers. Place them in a food processor and puree until smooth; reserve to the side.
In a heavy bottom medium pot, bring 8 cups water, salt and the roasted red pepper puree to a boil. Add the stone-ground cornmeal in a gentle stream, whisking or stirring vigorously in the same direction as you pour it in. Reduce the heat to medium-low and simmer, stirring continuously for 2 to 3 minutes. Cook the polenta, stirring every few minutes and scraping the bottom of the pan to prevent from sticking for 35 to 40 minutes. When the polenta is thick, glossy and pulling away from the side of the pan, add the Pecorino Romano and butter, stirring quickly to incorporate. Pour the polenta into a medium serving dish and serve immediately.
If you don't have a pressure cooker, you can cook the short ribs in a large Dutch oven in a 350 degree F oven for 2 1/2 hours. If your pressure cooker is not large, you can sear the short ribs in a large cast-iron pan before adding them to the pressure cooker. Deglaze the cast-iron pan with the bottle of wine and add the drippings to the pressure cooker also.