Preheat the oven to 350 degrees.
Next, bring a large pot of salted water to a boil and cook the pasta for about 5 minutes and drain.
After the pasta is done then add it to the casserole dish. Place the cooked chicken breasts and broccoli on top of the pasta.
Using the same pot, make the cheese sauce. Pour the chicken broth and milk into a medium pan. Wisk in the flour until it’s dissolved. Cook over medium heat until it is thick and bubbly, about 10 minutes or so. This can take more or less time, so just keep an eye on it and wish the sauce consistently to keep the milk or flour from burning at the bottom of the pot.
After the sauce starts to thicken then whisk in the onion powder, granulated garlic, dry mustard powder, salt, and pepper.
Stir in the cream cheese until it melts, about 5-7 minutes.
Slowly stir in the parmesan and shredded cheddar cheese until it melts, about 2-3 minutes. Taste for seasoning and stir in additional salt if you need to.
Pour the cheese mixture over the chicken, broccoli, and pasta. Stir until the sauce coats all of the ingredients. Set aside for a moment.
Into a small microwave-safe bowl, melt one tablespoon of butter in the microwave for about 25 seconds or it melts.
Stir in the panko crumbs into the melted butter.
Sprinkle the crumb mixture over the top of the casserole.
Bake uncovered for 35 - 45 minutes or until bubbly, and the top is brown.