Originally from Epicurious, but I've fiddled with the proportions a little. This is fast, filling, and flavorful, and nice with a good red wine.
1 lb Italian sausages, casings removed
1 onion, chopped
3 garlic cloves, chopped
1 28-oz can diced peeled tomatoes
1/3 C purchased pesto sauce
10 oz ziti or penne pasta (about 3 C), freshly cooked
8 C ready-to-use spinach leaves (about 2/3 of 10-ounce package)
6 oz mozzarella cheese, cubed
1 C grated Parmesan cheese (about 3 oz)
Heat heavy large saucepan over medium-high heat. Add sausage, onion and garlic and sauté until sausage is cooked through, breaking up meat with back of spoon, about 10 minutes. Add tomatoes with juices to pan. Simmer until sauce thickens slightly, stirring occasionally, about 10 minutes. Stir in pesto. Season sauce with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to simmer before continuing.)
Preheat oven to 375° F. Lightly oil 13 x 9-inch glass baking dish. Combine pasta, spinach, mozzarella and 1/3 cup Parmesan cheese in large bowl. Stir in hot tomato sauce. Transfer mixture to prepared baking dish. Sprinkle remaining ⅔ cup Parmesan cheese over. Bake until sauce bubbles and cheeses melt, about 30 minutes.