Sausage Spaghetti

Bring a large pot of water to a boil over high heat. Add pasta and cook according to package directions. Reserve 3/4 cup cooking water, then drain the pasta. 

Meanwhile, heat oil in a large skillet over medium-high heat. Add sausage; cook, breaking up chunks with a wooden spoon, until browned and cooked through, 5 to 7 minutes. Transfer the sausage to a plate, reserving the drippings in the pan. Add onion to the pan; cook over medium-high heat, stirring occasionally, until softened, about 3 minutes. Add red and yellow bell peppers; cook, stirring occasionally, until tender and golden on the edges, 2 to 3 minutes. Add garlic and crushed red pepper; cook, stirring constantly, until fragrant, about 1 minute. Reduce heat to medium-low. Stir in tomatoes, the cooked sausage, 1/2 cup reserved cooking water and tomato paste; cook, stirring occasionally, until reduced to a sauce-like consistency and tomatoes are very tender, 15 to 20 minutes. Stir in the pasta and basil. Add additional reserved cooking water, if needed, to reach desired consistency. Divide among 4 plates. Garnish with additional basil and serve with Parmesan, if desired.