In a shallow dish, combine the flour and Essence. Season the lamb liberally with salt and pepper, then dredge
the lamb shanks in the seasoned flour, shaking to remove any excess. In a large Dutch oven
, heat the 2 tablespoons olive oil and 2 tablespoons of the butter over medium-high heat until hot. Add the lamb shanks, in batches if necessary to prevent overcrowding, and cook until well-browned on all sides, 6 to 8 minutes. Remove the shanks from the pan and set aside. Add the onions
, carrots, and celery to the pan, and cook, stirring, until soft and caramelized around the edges, 4 to 6 minutes. Add the garlic
and cook, stirring, for 1 minute. Add the wine
and bring to a boil over high heat, stirring to deglaze
the pan. Cook until reduced by half. Add the tomatoes
and bay leaves and cook, stirring, for 1 minute. Add 2 tablespoons of the parsley, the rosemary, thyme, chicken broth, beef broth
, and reserved shanks and bring to a boil. Reduce the heat to a simmer
, season with salt and pepper, cover tightly, and cook, turning the meat occasionally, until the meat is tender and falling from the bone, 1 1/2 to 2 hours.
For the mascarpone polenta: In a large saucepan
, bring the water and milk
to a boil. Add the remaining 1/4 cup olive oil and season with salt and white pepper
. Very gradually, add the polenta in a steady stream, whisking constantly. Reduce the heat to low and cook, stirring frequently with a heavy wooden spoon until thick and creamy, 20 to 30 minutes. Add the heavy cream and mascarpone to the polenta and adjust the seasoning, to taste. Cook, covered, for 10 minutes longer, or until smooth, thick and creamy. Keep warm until ready to serve the shanks.
When the lamb shanks are very tender and beginning to fall from the bone, remove them from the braising liquid using a slotted spoon and transfer to a plate, cover with foil to keep warm, and set aside. Bring the braising liquid to a boil and cook until reduced to sauce consistency and thick enough to coat the back of a spoon. Adjust seasoning if necessary and remove from the heat.
To serve, spoon the polenta into 4 large bowls. Top each with a lamb shank and spoon the sauce over the lamb. Place the tips of the rosemary sprigs in an open flame until ignited; blow out the flames and garnish each plate with a smoking rosemary sprig.