Cook the penne pasta until al dente in salted boiling water. In the last three minutes, add broccoli florets. Reserve 1 cup of pasta water before draining.
In a large skillet, heat olive oil and butter, then sauté the diced onion for 4-5 minutes. Add minced garlic and cook for 30 seconds.
Pour in heavy cream and chicken broth, simmering for 2-3 minutes.
Remove from heat, whisk in Parmesan and mozzarella until smooth. Season with Italian seasoning, garlic powder, salt, pepper, and optional red pepper flakes.
Toss the drained pasta and broccoli into the skillet until evenly coated in the sauce.
Gently fold in shredded rotisserie chicken, adding reserved pasta water for desired consistency. Stir in a knob of cold butter before serving.
Plate the dish, garnishing with extra Parmesan or fresh herbs. Serve with salad or garlic bread.
Notes
Use reserved pasta water to achieve the perfect creamy texture. Feel free to swap in different cheeses or vegetables.