Campanelle Pasta with Sausage and Beans

Preheat oven to 400 °F. Cut off and discard top of garlic head to expose cloves, then wrap head in foil and roast in middle of oven until cloves are tender, about 45 minutes. Open foil carefully and cool to warm. Squeeze garlic from skins into a small bowl, then mash to a paste with a fork. Heat oil in a 12-inch heavy skillet over moderate heat until hot but not smoking, then cook sausage, stirring and breaking up large pieces, until browned, about 4 minutes. Add sliced garlic, shallot, and red pepper flakes and cook, stirring occasionally, until shallot is pale golden, about 2 minutes. Stir in tomatoes, beans, garlic paste, and stock and simmer, uncovered, stirring occasionally, until slightly thickened and reduced by half, 15 to 20 minutes. Meanwhile, cook pasta in a 6- to 8-quart pot of boiling salted water until al dente, then drain in a colander. Toss pasta with sausage mixture, parsley, basil, cheese, and salt to taste in a large bowl (or in pasta pot) until combined well. Serve with additional cheese, if desired.