1-First Step: Get the oven, pasta water, and baking dish ready Start by preheating the oven to 375°F. At the same time, bring a large pot of heavily salted water to a boil over medium-high heat. This gives you a strong base for the spaghetti, and the salted water helps season the pasta from the inside out. While the oven heats, set out a Dutch oven or a high-sided skillet, a baking dish, and your ingredients. Having everything nearby makes this Tuscan Baked Spaghetti much easier to manage, especially if you are cooking after a busy day. If you prefer, you can also shred the mozzarella ahead of time so the final assembly feels quick.

2-Second Step: Cook the spaghetti just shy of done Add 1 pound of dried spaghetti to the boiling water and cook it 1 minute less than the package says for al dente. This step matters because the pasta will keep cooking in the oven. If you cook it all the way through on the stovetop, it can turn soft after baking. Once the spaghetti is ready, drain it and set it aside. It does not need to sit for long, so move on to the sauce while it is still warm. This recipe works best when the pasta and sauce come together while both are hot enough to blend smoothly.

3-Third Step: Brown the sausage and build the base Melt 2 tablespoons unsalted butter in the Dutch oven or high-sided skillet over medium-high heat. Add 1 pound raw Italian sausage and cook until it is no longer pink, about 5 to 7 minutes. Break it up with a spoon as it cooks so it forms small, even pieces throughout the sauce. Once the sausage is browned, stir in the diced onion, sun-dried tomatoes, garlic, 1 1/2 teaspoons kosher salt, Italian seasoning, and black pepper. Cook this mixture for about 4 minutes, or until the onion softens. The pan will smell amazing at this point, and the tomatoes will start releasing their rich, tangy flavor into the sausage.

4-Fourth Step: Thicken the sauce Sprinkle 3 tablespoons all-purpose flour over the sausage mixture and cook for 1 minute. This quick step helps remove the raw flour taste and gives the sauce a smoother finish. Stir well so the flour coats the sausage and vegetables evenly. Slowly whisk in 4 cups of milk, a little at a time, so the sauce stays smooth. After all the milk is added, bring it to a boil, then reduce the heat and simmer for about 5 minutes. The sauce should thicken enough to cling to the pasta, but still remain creamy and spoonable.

5-Fifth Step: Add the spinach and combine everything Stir in 5 ounces of baby spinach and let it wilt into the sauce. If you are using a crowded pan, add the spinach in handfuls so it softens evenly. This adds freshness and color without changing the cozy flavor of the dish. Next, add the drained spaghetti to the sauce and toss until everything is well coated. Make sure the noodles are fully covered so every bite of this Tuscan Baked Spaghetti gets plenty of creamy sauce and savory sausage.

6-Sixth Step: Bake until bubbling and golden Transfer the spaghetti mixture to a baking dish and spread it out evenly. Top with 3 ounces of shredded low-moisture mozzarella cheese. The cheese melts into a light golden layer that gives the casserole its classic baked finish. Bake for 18 to 20 minutes, or until the sauce is bubbling and the cheese is melted. Let the dish cool for 5 minutes before serving so it has a chance to settle. If you want, sprinkle chopped fresh parsley over the top for a fresh, simple garnish.