Optional garnish: extra chopped fresh basil or other fresh herbs
Instructions
Preheat oven to 375°F. Grease a 9 x 13-inch baking dish with nonstick spray; set aside.
Boil penne in a large pot of well salted boiling water according to package directions for al dente. Drain.
Meanwhile, brown sausage and onion in a large skillet or Dutch oven over medium-high heat until the sausage is no longer pink and the onion is translucent, about 5-7 minutes. Add the garlic and cook for 1 more minute. Drain off excess grease.
Stir in the marinara; simmer for about 10 minutes. Add the pesto and crushed red pepper flakes. Taste the sauce and season with salt and pepper, if desired. Stir in the cooked pasta, spinach, and fresh basil.
Spread half of the pasta mixture in the prepared baking dish. Sprinkle with half of the Italian cheese and half of the Parmesan cheese. Top with the remaining pasta mixture. Add the rest of the Italian cheese and the rest of the Parmesan cheese on top.
Bake, uncovered, for about 25-30 minutes, until the cheese on top is melted and the inside is hot and bubbly. Garnish with additional fresh basil, if desired.
Swap out the Italian sausage and use ground beef, ground turkey, ground chicken, or a chicken or turkey-based Italian sausage.
Any short pasta shape will work. For instance, replace the penne with rotini, farfalle, rigatoni, or ziti.
Omit the spinach if your family doesn't care for it. You can also sub with a 10-ounce package of frozen chopped spinach. Just make sure that you thaw the frozen spinach and squeeze it really dry before adding it to the pasta mixture. Alternatively, sub with other veggies like diced zucchini (sauteed with the onion and sausage) or parboiled broccoli.
Add other fresh or dried herbs for even more flavor. Good options include oregano, thyme, and rosemary. Italian seasoning is also a convenient way to get a lot of extra flavor into the dish.
Feeding a smaller family? Cut the ingredients in half and bake the casserole in a 2-quart casserole dish.