Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add the penne pasta and cook it until al dente, about 10 minutes. In the last 3 minutes of cooking, carefully add the broccoli florets.

Before draining the pasta and broccoli, reserve 1 cup of the starchy pasta water. Drain them in a colander and set aside.

In a large skillet, heat 2 tablespoons of olive oil and 2 tablespoons of unsalted butter. Add the diced yellow onion and sauté for about 4-5 minutes. Stir in the minced garlic and cook for an additional 30 seconds.

Pour in 1 cup of heavy cream and 1 cup of low-sodium chicken broth into the skillet, stirring to combine. Let the mixture simmer gently for 2-3 minutes.

Off the heat, mix in 1 cup of freshly grated Parmesan cheese and 1 cup of shredded mozzarella cheese. Season with Italian seasoning and garlic powder.

Gently fold the drained pasta and broccoli back into the creamy sauce, adding the shredded rotisserie chicken. Incorporate reserved pasta water for desired consistency.

Finish by stirring in a cold knob of butter and serve warm, garnished with additional cheese or herbs if desired.