Spinach, Bell Pepper, and Sausage Pasta

1 pound Nature’s Farm penne pasta
Salt and pepper
1 pound hot italian sausage, casings removed
1 red bell pepper, stemmed, seeded, and cut into 1/2-inch pieces
4 tablespoons unsalted butter
5 ounces (5 cups) baby spinach
1 ounce Parmesan cheese, grated (1/2 cup), plus extra for serving
1. Bring 4 quarts water to boil in Dutch oven. Add pasta and 1 tablespoon salt to water and cook until al dente. Reserve 1 cup pasta cooking water, then drain pasta. Return pasta to pot.
2. Meanwhile, cook sausage in 12-inch nonstick skillet over medium heat, breaking up pieces with spoon, until cooked through, about 10 minutes. Add bell pepper and cook, stirring occasionally, until beginning to brown, about 5 minutes. Remove from heat and stir in butter.
3. Add sausage mixture, spinach, Parmesan, and ½ cup reserved pasta cooking water to pasta and toss to combine, adding additional reserved water as needed. Season with salt and pepper to taste. Serve, passing extra Parmesan separately.