Follow these steps carefully to build layers of flavor, resulting in a perfectly balanced and incredibly delicious chicken alfredo. The key is to have your ingredients prepped and ready to go (a process known as mise en place) before you start cooking.

1. Cook the Pasta: Bring a large pot of heavily salted water to a rolling boil. Add the fettuccine and cook according to package directions until al dente (firm to the bite). Just before draining, reserve about 1 cup of the starchy pasta water. Drain the pasta and set it aside. Do not rinse the pasta; the starch on its surface helps the sauce cling to it.
2. Prepare and Cook the Chicken: While the pasta is cooking, pat the chicken breast cubes dry with a paper towel. In a small bowl, toss the chicken with paprika, garlic powder, salt, and black pepper until evenly coated. Heat 2 tablespoons of butter in a large, deep skillet or Dutch oven over medium-high heat. Once the butter is melted and foaming, add the seasoned chicken in a single layer. Cook for 5-7 minutes, turning occasionally, until golden brown on all sides and cooked through (internal temperature should reach 165°F or 74°C). Remove the chicken from the skillet and set it aside on a plate.
3. Sauté the Vegetables: In the same skillet, add the 1 tablespoon of olive oil. Add the sliced red bell pepper and broccoli florets. Sauté for 4-5 minutes until they are tender-crisp. You want them to retain a slight bite. Add the sliced mushrooms and cook for another 3-4 minutes until they have released their moisture and started to brown. Finally, add the fresh spinach and cook for 1-2 minutes, stirring until it has just wilted. Remove all the vegetables from the skillet and set them aside with the cooked chicken.
4. Start the Alfredo Sauce: Reduce the heat to medium-low. In the now-empty skillet, melt the 4 tablespoons of unsalted butter. Add the minced garlic and cook for about 30-60 seconds until fragrant. Be very careful not to let the garlic burn, as it will become bitter.
5. Create the Roux and Build the Sauce: Sprinkle the all-purpose flour over the melted butter and garlic. Whisk constantly for 1-2 minutes to cook out the raw flour taste. This mixture is called a roux, and it is the foundation for a thick and creamy sauce. Slowly—and this is a crucial step—pour in the warmed milk while whisking vigorously to prevent any lumps from forming. Once the milk is fully incorporated and the mixture is smooth, slowly whisk in the warmed heavy cream.
6. Finish the Sauce and Melt the Cheese: Bring the sauce to a gentle simmer, stirring occasionally, and let it cook for 2-3 minutes until it has thickened slightly. It should be thick enough to coat the back of a spoon. Reduce the heat to the lowest possible setting. It’s important that the sauce is not boiling when you add the cheese. Gradually add the freshly grated Parmesan cheese, a handful at a time, whisking continuously until the cheese is completely melted and the sauce is smooth and velvety. Stir in the nutmeg, salt, and white pepper. Taste and adjust seasoning as needed.
7. Combine Everything: To the skillet with the finished Alfredo sauce, add the cooked pasta, the cooked chicken, and the sautéed vegetables. Use a pair of tongs to gently toss everything together until the pasta, chicken, and vegetables are thoroughly coated in the creamy sauce. If the sauce seems too thick, add a splash of the reserved pasta water, a tablespoon at a time, until it reaches your desired consistency.
8. Serve Immediately: Serve the Veggie-Loaded Chicken Alfredo Pasta hot, garnished with a sprinkle of extra Parmesan cheese and some freshly chopped parsley for a touch of freshness and color.