Cup of Yum
1. Preheat oven to 400 degrees F.
2. Lightly grease a 9 x 13-inch baking dish with cooking oil spray or butter and set aside.

Make the creamy sauce

Cup of Yum
1. Place a medium cast iron skillet or saucepan over medium-high heat. Once the skillet is hot, add the butter and melt it.
2. Add onion and garlic and sauté until just the garlic is fragrant, and onion is soft.
3. Whisk in flour and cook for 2 minutes, stirring continuously.
4. Reduce heat to low, slowly and gradually whisk in 1 cup of chicken broth until fully combined.
5. Again, gradually, without rushing, stir in milk and cream, until fully combined. Stir in dried thyme, paprika, salt, and pepper.
6. With the heat on low, let the sauce gently simmer (NOT boil) for 2-3 minutes,  until it starts to thicken. Remove from heat and set aside.
7. Pour half of the cream sauce over the potatoes, and top with 1 cup of mozzarella cheese, distribute evenly.

Assemble the casserole

1. Arrange the remaining potatoes and pour the remaining cream sauce on top. Sprinkle the remaining cheddar cheese and Parmesan cheese on top if desired.
2. Cover the baking dish with aluminum foil and bake in the preheated oven for 40 minutes. Until the potatoes are just tender and the sauce is bubbly.
3. Remove foil and continue to cook for another 20-30 minutes, or until the potatoes are fully done and the top is a golden-brown color.
4. Before removing from the oven, broil for a few minutes to brown the cheese on top. Watch to not burn it.
5. Garnish with chopped parsley or chopped green onions. Serve warm.