Bring a large pot of salted water to a boil. Add the penne pasta and cook for 8-10 minutes or until al dente. In the last 3 minutes, add the broccoli florets. Reserve 1 cup of the pasta water, drain and let steam escape.

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

Pour in heavy cream and chicken broth. Stir gently and let simmer for 2-3 minutes without boiling.

Remove from heat and whisk in parmesan and mozzarella until melted. Season with Italian seasoning, garlic powder, and red pepper flakes.

Return pasta and broccoli to skillet, toss gently to coat with sauce. Fold in shredded rotisserie chicken, adding reserved pasta water as needed for creaminess.

Stir in a knob of cold butter before serving for richness. Serve warm and enjoy!