Pre-heat the oven to 375ºF.
Place a large, heavy-bottomed pan over medium-high heat with 2 tablespoons EVOO, about two turns of the pan. Generously season all sides of the short ribs with salt, pepper and flour. When the pan is scorching hot, add the short ribs to the pan and sear them until deep golden brown all over, 4-5 minutes per side.
Once all of the short ribs have been seared off, add half the bottle of pomegranate juice, paprika, allspice and bay leaf to the pan. Scrape up all the golden brown bits from the bottom of the pan and bring the juice up to a bubble. Boil until it reduces by about half.
Add in 1 quart of beef stock and return the seared ribs to the pot. Cover and transfer the pot to the oven. Braise until the ribs are very tender, about 2 hours, leaving the pot covered and undisturbed.
After the ribs have been braising for an hour, place the beets onto a baking sheet. Drizzle them lightly with EVOO and season with salt and freshly ground black pepper. Place them into the oven along with the ribs and roast until tender, about 45 minutes. Remove from the oven and let cool until you can handle them, about 10 minutes. Rub the beets lightly to remove their skin, then cut them into quarters and reserve.
30 minutes before the ribs are done, add the onions, celery and carrots to the braising pot and replace the cover.
When the meat has about 20 minutes left to cook, place a medium size pot over medium-high heat and melt 2 tablespoons of butter. Add the sage and cook it until aromatic and lightly golden, 2-3 minutes. Add the milk and chicken stock to the pot and bring to a boil. When the liquids are boiling, whisk in the polenta. Cook, continuing to whisk, until thickened, 2-3 minutes. Season the polenta with nutmeg, grated Parmigiano Reggiano cheese, salt and freshly ground black pepper.
In a medium-size skillet over medium-high heat, melt 2 tablespoons of butter. Stir in the flour, cook it about 1 minute, then whisk in the remaining 1/2 bottle of pomegranate juice and 2 cups of beef stock. Season with salt and freshly ground black pepper.
When the ribs are done braising, remove the pot from the oven and transfer the meat to a serving plate. Add the gravy to the braising liquid and reduce it over medium-high heat until it is thick. Stir the quartered beets into the sauce in the pot and pour it over the short ribs. Garnish the serving plate with lemon juice, EVOO-dressed beet greens and pomegranate seeds. Serve the polenta alongside.