Chef Renee Scharoff likes to serve this fragrant lamb with creamy whipped potatoes and a garnish of fresh chopped thyme leaves.
Preheat the oven to 400 degrees F. In a large Dutch oven, cook the bacon in the oil. When it is crisp, remove it with a slotted spoon, leaving the fat behind. Put the bacon on paper towels to drain.
Season the lamb generously with salt and pepper. Sear the shanks on all sides until brown. Remove them and set them aside. Add the onions and carrots to the pot and let them sweat over low heat for 10 minutes, or until the onions are soft and a bit browned. Season with salt and pepper. Add the garlic and cook for 1 minute. Stir in the tomato paste, then pour in the wine and let the mixture simmer for 2 to 3 minutes to cook off the alcohol. Add the stock and herb bouquet. Add back the lamb and bacon, making sure the lamb is covered with stock. Bring to a boil and cook for 5 minutes.
Reduce the oven to 325 degrees F. Cover the pot and put it in the oven. Braise the lamb for about 90 minutes. Add the mushrooms and turn the shanks in the sauce so that they cook evenly. Braise for another 60 minutes, until they are very tender. Remove the shanks to a platter and put the pot over medium heat.
In a small pot, melt the butter and whisk in the flour to make a roux. Stir it into the sauce to thicken it. Serve each shank with some of the sauce and vegetables.
If you do not have a Dutch oven, use a pot with a tight fitting lid that can be put into the oven.