Bring a large pot of salted water to a rolling boil over high heat. Add the penne pasta and cook it until al dente, about 8-10 minutes. Three minutes before the pasta is done, gently stir in the broccoli florets.

Before draining, scoop out 1 cup of the starchy pasta water. Drain pasta and broccoli together.

In a large skillet, heat olive oil and butter over medium-low heat. Add diced onion and sauté until softened, about 4-5 minutes. Add minced garlic and sauté for 30 seconds.

Reduce heat to low, pour in heavy cream and chicken broth, and gently simmer for 2-3 minutes.

Remove from heat and whisk in Parmesan and mozzarella cheese until melted. Stir in Italian seasoning and garlic powder.

Fold in the drained pasta and broccoli. Add shredded rotisserie chicken and incorporate reserved pasta water until desired consistency.

Stir in a knob of cold butter before serving. Adjust seasoning and enjoy!