Bring a large pot of salted water to a boil and cook the penne pasta according to the package directions until al dente.

During the last 3 minutes of cooking time, add the broccoli florets directly to the pasta water.

Before draining, reserve 1 cup of starchy pasta water in a measuring cup. Then drain the pasta and broccoli together, and set aside.

Heat olive oil and butter in your largest skillet over medium-low heat. Cook the diced onion for 4-5 minutes until softened.

Add the minced garlic and cook for 30 seconds until fragrant.

Pour in the heavy cream and chicken broth, bringing the mixture to a gentle simmer for 2-3 minutes. Look for small bubbles around the edges; do not let it boil.

Remove the skillet from heat completely before adding cheese to prevent graininess.

Whisk in the Parmesan and mozzarella until completely smooth. Then season with Italian seasoning, garlic powder, salt, pepper, and red pepper flakes.

Add the drained pasta and broccoli to the creamy sauce, tossing gently with tongs to coat everything evenly.

Fold in the shredded rotisserie chicken last.

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

Stir in a cold knob of butter just before serving for an extra touch of richness.

Serve this creamy pasta in bowls, garnished with extra Parmesan cheese and a sprinkle of red pepper flakes if desired.

You can also accompany it with a simple green salad or garlic bread for a complete meal.