Ingredients

• 1 quart reduced-sodium chicken broth
• 1 quart water
• 1 bunch broccoli rabe
• 1/4 cup olive oil
• 1 medium onion, chopped
• 2 garlic cloves, chopped
• 1 lb medium pasta shells
• 1/2 cup grated Parmigiano-Reggiano

Instructions

1. Bring broth, water, and 1 teaspoon salt to a boil in a medium saucepan, then reduce heat and keep at a bare simmer.
2. Trim tough stem ends from broccoli rabe, then cut remaining stems crosswise into 1-inch pieces and reserve. Coarsely chop florets and leaves.
3. Heat oil in a 5- to 6-quart heavy pot over medium-high heat until it shimmers, then sauté onion with 1/2 teaspoon salt until softened, 3 to 5 minutes. Stir in garlic and sauté 1 minute, then add pasta, broccoli rabe stems, and 3/4 cup hot broth and simmer briskly, stirring constantly, until broth is absorbed. Continue simmering and adding hot broth, about 3/4 cup at a time, stirring frequently and letting each addition be absorbed before adding the next, until pasta is almost al dente and creamy-looking, 12 to 13 minutes. Stir in remaining broccoli rabe and 1/4 teaspoon pepper and cook, stirring, until pasta is al dente and broccoli rabe is just tender, 2 to 3 minutes. (If needed, add more hot broth to moisten; there will be some broth left over.) Stir in cheese and salt and pepper to taste. Serve with more cheese on the side.