Scrub and clean potatoes, then thinly slice potatoes into 1/8 inch thin slices. No need to peel potatoes. Set aside.

Pre-heat oven to 350 degrees F.

In a medium pot, turn heat to medium and add butter. Once butter is melted, add diced onions and minced garlic. Sauté for 1-2 minute or until they are soft. Avoid over-browning them.

Add flour and stir to combine. Once combined, add milk, chicken broth, thyme and salt. Stir and bring to a boil. Continue stirring and cook for a few minutes, or until sauce thickens slightly.

Turn off heat and add shredded cheddar, shredded mozzarella and parmesan. Stir to combine. It’s okay if cheese does not melt completely.

Grease a 9″ x 13″ casserole. Add 1/3 of the potatoes to casserole, then spread 1/3 of the cheese sauce onto potatoes, then add the next 1/3 of potatoes and cheese sauce, until all the potatoes and cheese are layered. There should be three alternate layers of potatoes and cheese sauce.

Cover casserole with aluminum foil, bake for 30 minutes. Uncover casserole and bake for another 35-45 minutes.

Cool for 10 minutes. Serve and enjoy!