How to Make It
Preheat the oven to 350°. Season the rabbit inside and out with salt and pepper and stuff the cavity with two-thirds of the herb sprigs. Arrange the remaining sprigs on top. Wrap the rabbit in the pancetta strips, making sure the loin and legs are covered. Using cotton string, tie the rabbit at 2-inch intervals to secure the pancetta. Set the rabbit in a roasting pan and roast for 30 minutes. Turn, baste with the wine and cook for about 30 more minutes, or until the juices run clear with a thigh is pierced; the meat will be pink around the joints. Let cool.
Finely chop enough of the cooked pancetta to equal 1/3 cup. Discard the remaining pancetta and the herbs. Remove the rabbit meat from the bones and cut it into 3/4-inch pieces.
In a small saucepan of boiling salted water, blanch the fava beans for 1 minute. Drain the beans and rinse with cold water. Peel off and discard the tough bean skins.
In a medium saucepan of boiling salted water, cook the penne until al dente, about 1 minutes; drain the pasta and toss with 1 tablespoon of the butter.
Meanwhile, in another large saucepan, bring the chicken stock to a boil. Add the fava beans and simmer over moderately low heat until they are tender, about 3 minutes. Add the reserved pancetta and the rabbit and cook over moderately high heat, stirring, until the stock is almost completely absorbed, about 2 minutes. Removed from the heat and stir in the pasta, the mascarpone and the remaining 1 tablespoon of butter. Season with salt and pepper and serve at once.