Melt 1 tbsp of butter in a large sauté pan over medium high heat. Sauté the chicken, onion, and mushrooms for 8 minutes.
Add in the cooked rice. Break up any clumps. Cook for 2 minutes.
Make a hole in the center of the rice. Squirt a 1/4 cup of ketchup in the center. Allow to cook for a minute before mixing in.
Mix in the ketchup. Season with salt and pepper. Cook for 2 more minutes. Set aside.
Melt 3 tbsp of butter in a small pot over medium heat. Add in the flour. Whisk until all lumps are broken up. Cook for 3 minutes, continuously stirring.
Pour in the heavy cream.
Cook for 5 minutes, continuously whisking until the cream sauce has thickened. Season with salt and white pepper.
Preheat the oven to 425 degrees. Grease a round baking dish. Add in the rice.
Pour the cream sauce over the rice.
Top the cream sauce with mozzarella and parmesan cheese.
Bake for 10-12 minutes until the cheese is bubbly. Let rest for 10 minutes before serving.