Bring a large pot of salted water to boil, and cook the penne according to package directions until al dente. In the last three minutes of cooking, add your broccoli florets to the pot.

Before draining, reserve 1 cup of starchy pasta water. Drain the pasta and broccoli together, setting them aside.

In your largest skillet, heat the olive oil and butter over medium-low heat.

Add the diced onion and cook for about 4-5 minutes until softened.

Stir in the minced garlic and cook for another 30 seconds until fragrant.

Pour in the heavy cream and chicken broth, bringing the mixture to a gentle simmer. Look for small bubbles around the edges, but avoid a rolling boil.

Remove the skillet from heat to prevent graininess, then whisk in the Parmesan and mozzarella cheese until you achieve a completely smooth sauce.

Season with Italian seasoning, garlic powder, salt, pepper, and red pepper flakes.

Toss the drained pasta and broccoli into the creamy sauce.

Gently fold in the shredded rotisserie chicken.

Gradually add reserved pasta water two tablespoons at a time until you reach a creamy, glossy consistency.

For that restaurant-quality finish, stir in a cold knob of butter just before serving.