1-First Step: Get everything ready Heat the oven to 375 degrees Fahrenheit. Bring a large pot of heavily salted water to a boil over medium-high heat. While the water heats, measure and chop your onion, garlic, sun-dried tomatoes, and parsley if you are using it. This kind of quick mise en place makes the whole cooking process feel calmer.

2-Second Step: Cook the spaghetti just short of al dente Add 1 pound of dried spaghetti noodles to the boiling water and cook for 1 minute less than the package directions for al dente. The pasta will keep cooking in the oven, so this small step keeps it from turning mushy later. Once it is ready, drain it and set it aside while you finish the sauce.

3-Third Step: Brown the sausage Melt 2 tablespoons unsalted butter in a Dutch oven or high-sided skillet over medium-high heat. Add 1 pound of raw Italian sausage with the casings removed. Cook it while breaking it up with a spoon until it is no longer pink, which usually takes 5 to 7 minutes. The browned bits at the bottom help build a deeper flavor in the sauce.

4-Fourth Step: Add the onion, tomatoes, garlic, and seasonings Stir in the diced yellow onion, sun-dried tomatoes, minced garlic, 1 1/2 teaspoons kosher salt, Italian seasoning, and black pepper. Cook for about 4 minutes, or until the onion starts to soften. At this point, the pan should smell rich, savory, and a little sweet from the tomatoes.

5-Fifth Step: Thicken the sauce Sprinkle 3 tablespoons all-purpose flour over the sausage mixture and stir for 1 minute. This helps remove the raw flour taste and gives the sauce body. Then slowly whisk in 4 cups of milk, a little at a time, so the sauce stays smooth instead of lumpy.

6-Sixth Step: Simmer until creamy Bring the sauce to a boil, then lower the heat and simmer for about 5 minutes. The sauce should thicken slightly and look silky. If you want a richer sense of the tomato ingredient in the meal, you can pair this with another tomato-forward dish like this strawberry shortcake crunch cake recipe for a sweet finish to dinner later in the week.

7-Seventh Step: Wilt the spinach Stir in 5 ounces of baby spinach, which is about 5 packed cups, until it wilts into the sauce. The green leaves will shrink fast, adding color and a fresh taste without making the dish feel heavy.

8-Eighth Step: Combine with the pasta Add the drained spaghetti to the sauce and toss until everything is coated. Taste and add more salt if needed. The goal here is a pasta mixture that looks creamy but not soupy, with the sauce clinging to every strand.

9-Ninth Step: Bake until bubbly Transfer the pasta mixture to a 9×13-inch baking dish. Sprinkle the top with 3 ounces of shredded low-moisture mozzarella cheese. Bake for 18 to 20 minutes, or until the edges bubble and the cheese melts. The top should look lightly golden and inviting.

10-Final Step: Rest and serve Let the baked spaghetti cool for about 5 minutes before serving. This short rest helps the sauce settle, so it is easier to scoop. Finish with finely chopped parsley if you want a fresh pop of color.