Pasta with Lentils and Arugula

Ingredients

• 2 tablespoons olive oil
• 2 large onions halved and thinly sliced (4 cups)
• coarse salt and ground pepper
• 12 ounces plum tomatoes cored and diced (about 2 cups)
• 3/4 cup lentils picked over and rinsed
• 12 ounces orecchiette pasta
• 1 bunch (8 ounces) arugula stemmed and coarsely chopped
• 1/2 cup finely grated Parmesan cheese plus more for serving (optional)

Instructions

1. 1
   Heat oil in a large skillet over medium-low heat. Add onions and ½ teaspoon salt; cover, and cook until onions wilt, about 20 minutes. Uncover; raise heat to medium. Cook, stirring often, until onions are dark brown, 20 to 25 minutes more.
2. 2
   Add ¼ cup water; stir to loosen any browned bits from pan. Stir in tomatoes; remove from heat.
3. 3
   Meanwhile, in a medium saucepan, cover lentils with water by 1 inch. Bring to a simmer. Cover; cook until lentils are tender but still holding their shape, 15 to 20 minutes. Drain; stir into onion mixture. Season with salt and pepper.
4. 4
   Cook pasta in a pot of salted water until al dente. Reserve 1 cup pasta water; drain pasta, and return to pot.
5. 5
   Add lentil mixture, arugula, cheese, and reserved pasta water; toss. Season with salt and pepper. Serve with more cheese, if desired.