Sausage and Mushroom Penne Gratin

Preparation

1. Step 1

   Cook penne in a pasta pot of boiling salted water (2 tablespoons salt for 6 quarts water) until al dente. Reserve 1/2 cup pasta-cooking water, then drain pasta and transfer to a flameproof 3-quart baking dish.

   Step 2

   Preheat broiler.

   Step 3

   Meanwhile, cook sausage in 1 tablespoon oil in a 12-inch nonstick skillet over high heat, stirring occasionally and breaking up any large pieces, until no longer pink. Transfer with a slotted spoon to a bowl, leaving fat in skillet.

   Step 4

   Add remaining tablespoon oil to skillet along with mushrooms and garlic, then cook over high heat, stirring occasionally, until mushrooms are golden, about 3 minutes.

   Step 5

   Return sausage to skillet along with cream, reserved 1/2 cup cooking water, a rounded 1/4 teaspoon salt, and 1/4 teaspoon pepper and boil over high heat, stirring once or twice, until thickened, about 4 minutes. Pour over pasta, then stir in Parmigiano-Reggiano, 1/2 cup mozzarella, and salt to taste. Spread evenly in baking dish and top with remaining mozzarella.

   Step 6

   Broil 3 to 4 inches from heat until golden brown in spots, about 5 minutes.