| 1 pound | Collard greens (about 12 cups), stripped from thick stems, washed, dried and coarsely chopped (1/2 inch pieces) |
| 2 ounces | Sliced pancetta or bacon, finely diced (3/4 cup) |
| 2 tsp | Extra-virgin olive oil |
| 1 | Medium onion, chopped |
| 2 cloves | Garlic, minced |
| 1/8 tsp | Crushed red pepper |
| 1 28 ounce | Can diced tomatoes (not drained) |
| 1/4 cup | Water |
| 8 ounces | Medium pasta shells (3 cups) |
| 1/4 tsp | Salt, or to taste |
| | Freshly ground pepper to taste |
| 1/2 cup | Freshly grated Parmigiano-Reggiano cheese |
1. Bring 2 cups lightly salted water to a boil in a large wide pan. Add collards and cook until tender, 10 to 12 minutes. Drain, rinse with cold water and press out excess moisture. Set aside.
2. Put a large pot of lightly salted water on to boil for cooking pasta.
3. Cook pancetta (or bacon) in a large nonstick skillet over medium heat, stirring often, until golden, 5 minutes. Drain; discard fat.
4. Add oil to the skillet and heat over medium heat. Add onion and cook, stirring often, until softened, 3 to 5 minutes. Add garlic and crushed red pepper; cook, stirring, for 30 to 60 seconds. Add pancetta (or bacon), tomatoes and water; bring to a simmer, mashing the tomatoes with a potato masher or the side of a wooden spoon. Reduce heat to medium-low and simmer, uncovered, until thickened, about 20 minutes.
5. About 10 minutes before the sauce is ready, cook pasta in the boiling water, stirring often, until just tender, 8 to 10 minutes. Drain pasta, reserving 1/4 cup of the cooking water.
6. Add the pasta, collards and reserved pasta-cooking water to the tomato sauce. Heat, stirring, until the pasta has absorbed some of the flavors, about 1 minute. Season with salt and pepper. Spoon into pasta bowls, sprinkle with cheese and serve.