Follow these step-by-step instructions carefully to achieve a perfectly cooked, incredibly flavorful one-pot meal. The key is to build layers of flavor in the same pot, from searing the chicken to simmering the pasta.

1. Prepare and Sear the Chicken: Begin by patting your chicken breast cubes dry with a paper towel; this is crucial for getting a good sear. Season them generously with ½ teaspoon of salt and ½ teaspoon of black pepper. Heat the olive oil in a large Dutch oven or a heavy-bottomed pot over medium-high heat. Once the oil is shimmering, add the chicken cubes in a single layer, being careful not to overcrowd the pot (work in batches if necessary). Sear the chicken for 2-3 minutes per side, until it’s golden brown and cooked through. The goal here is not just to cook the chicken, but to develop a flavorful brown crust. This process, known as the Maillard reaction, creates deep, savory notes that will form the foundation of your sauce. Once browned, remove the chicken from the pot with a slotted spoon and set it aside on a plate.
2. Sauté the Aromatics: Reduce the heat to medium. To the same pot, add the finely chopped yellow onion. Sauté for 3-4 minutes, stirring occasionally, until the onion has softened and become translucent. Use your spoon to scrape up any browned bits (fond) left from the chicken; these are packed with flavor. Next, add the minced garlic and Italian seasoning. Cook for another 60 seconds, stirring constantly until the garlic is fragrant. Be very careful not to let the garlic burn, as it will become bitter and ruin the sauce. This step of “blooming” the aromatics in the hot oil releases their essential oils and deepens their flavor.
3. Combine Liquids and Pasta: Pour in the 4 cups of low-sodium chicken broth, bringing it to a simmer. As it heats up, use your wooden spoon or spatula to deglaze the pot, which means scraping up any remaining browned bits from the bottom. This is a critical flavor-building step. Once the broth is simmering, add the uncooked penne pasta. Stir everything together well, ensuring the pasta is fully submerged in the broth.
4. Simmer and Cook: Bring the mixture to a steady simmer, then reduce the heat to medium-low. Cover the pot and let it cook for 10-12 minutes, or until the pasta is al dente (cooked through but still with a slight bite). It’s important to stir the pasta every 2-3 minutes to prevent it from sticking to the bottom of the pot and to ensure it cooks evenly. The pasta will absorb most of the chicken broth, and the starches it releases will begin to naturally thicken the sauce.
5. Create the Creamy Sauce: Once the pasta is al dente and most of the liquid has been absorbed, reduce the heat to low. Slowly pour in the heavy cream and sprinkle in the grated Parmesan cheese. Stir gently but continuously until the cheese has completely melted and the sauce has become smooth, creamy, and velvety. It’s crucial to do this over low heat to prevent the cream from curdling or the cheese from clumping. Season the sauce with the remaining ½ teaspoon of salt and ½ teaspoon of black pepper. Taste the sauce at this point and adjust the seasoning if necessary.
6. Final Touches: Return the cooked chicken back to the pot. If you are using spinach, add the fresh spinach now. Stir everything together until the chicken is heated through and the spinach has wilted down into the sauce, which should only take about 1-2 minutes. The residual heat is more than enough for this step.
7. Serve and Garnish: Turn off the heat. Immediately ladle the hot, creamy pasta into shallow bowls. Garnish generously with freshly chopped parsley and an extra sprinkle of grated Parmesan cheese, if desired. Serve immediately and enjoy the fruits of your one-pot labor.