1-First Step: Get everything ready and preheat the oven Start by heating your oven to 375°F. This gives it time to reach the right temperature while you cook the pasta and sauce. Put a large pot of heavily salted water on the stove and bring it to a boil over medium-high heat. A well-salted pot gives the spaghetti better flavor from the inside out. At the same time, gather the rest of your ingredients so the cooking process stays smooth. Dice the onion, mince the garlic, measure the milk, and shred the mozzarella if needed. Since Tuscan Baked Spaghetti moves quickly once the sausage hits the pan, having everything ready saves stress later.

2-Second Step: Cook the spaghetti just shy of al dente Add 1 pound of dried spaghetti noodles to the boiling water and cook it 1 minute less than al dente according to the package directions. This matters because the pasta will continue cooking in the oven, and slightly undercooked noodles keep the final dish from turning soft or mushy. Once the spaghetti is ready, drain it and set it aside briefly. Do not rinse it, since the starch helps the sauce cling better. If you are using gluten-free pasta, watch the cooking time closely because it can become too soft faster than regular spaghetti.

3-Third Step: Brown the sausage and build the flavor base While the pasta cooks, melt 2 tablespoons of unsalted butter in a Dutch oven or high-sided skillet over medium-high heat. Add 1 pound of raw Italian sausage, breaking it into small pieces as it cooks. Let it brown until no longer pink, which should take about 5 to 7 minutes. Next, stir in the diced yellow onion, sun-dried tomatoes, minced garlic, 1 and a half teaspoons kosher salt, dried Italian seasoning, and black pepper. Cook for about 4 minutes, just until the onion softens. This stage gives Tuscan Baked Spaghetti its deep savory base and that rich tomato scent that fills the kitchen.

4-Fourth Step: Thicken the creamy sauce Sprinkle 3 tablespoons of all-purpose flour over the sausage mixture and stir constantly for 1 minute. This helps cook out the raw flour taste and sets up the sauce so it thickens properly. Slowly whisk in 4 cups of milk, a little at a time, so the sauce stays smooth instead of clumping. Bring the mixture to a boil, then lower the heat and simmer for about 5 minutes. You want it slightly thickened, not overly dense. The sauce should coat a spoon lightly and still move easily when stirred. If you are using a lower-fat milk, keep the heat steady and stir a bit more often to avoid scorching.

5-Fifth Step: Add the spinach and finish the filling sauce Stir in the baby spinach a handful at a time until it wilts into the sauce. This usually happens fast, and the leaves will shrink down more than you expect. The spinach adds freshness and color, and it also balances the richness of the sausage and milk sauce. If the sauce tastes a little flat at this point, add a pinch more salt. Different sausages and sun-dried tomatoes vary in saltiness, so tasting before mixing with the pasta is a smart move. That small check helps your Tuscan Baked Spaghetti taste balanced instead of overly salty.

6-Sixth Step: Combine the pasta and sauce Return the drained spaghetti to the pot it cooked in, then pour the sauce over the noodles. Toss until every strand is coated. The creamy sauce should cling to the pasta and distribute the sausage, spinach, onion, and tomatoes evenly through the whole batch. This is a good moment to see if the mixture feels a little loose or tight. If it seems too thick, you can loosen it with a splash of milk. If it feels too thin, give it another minute or two over low heat before transferring it to the baking dish.

7-Seventh Step: Assemble and bake Transfer the pasta mixture to a 9 by 9-inch baking dish that is at least 2 inches high, or use a 9 by 13-inch dish if you want a thinner layer. Spread it out evenly, then top with 3 ounces of shredded low-moisture mozzarella. The cheese melts into a soft golden layer that finishes the dish beautifully. Bake at 375°F for 18 to 20 minutes, or until the casserole is bubbling and the cheese has melted. If you prefer a deeper top, let it bake a minute or two longer, but keep an eye on it so the sauce does not dry out. The goal is a creamy center with a lightly set top.

8-Final Step: Rest, garnish, and serve Take the dish out of the oven and let it cool for about 5 minutes. This short rest helps the sauce settle, so each serving holds together better on the plate. If you like, sprinkle on finely chopped fresh parsley for a fresh finish. Serve Tuscan Baked Spaghetti warm and enjoy the mix of creamy sauce, savory sausage, soft pasta, and cheesy top. It is a full meal on its own, so you can keep the rest of dinner simple. For a sweet ending after the pasta, you might also like to browse a few fun snack ideas such as pink popcorn for parties.