Return the seared ribs to the pot and add in 1 quart of beef stock. 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, drizzle the beets lightly with EVOO and season with salt and freshly ground black pepper. Wrap them each in foil and 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, carrots and bay leaf to the braising pot and replace the cover.
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 is done braising, remove the pot from the oven and transfer the meat and veggies to a serving plate. Add the gravy to the braising liquid and reduce over medium-high heat until it is thick.
Just before serving, 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.
To serve, ladle some polenta into the bottom of a large, shallow bowl. Place two ribs and some of the braised veggies on top of the polenta and pour the gravy over everything. Garnish each serving with some of the EVOO-dressed beet greens and pomegranate seeds.