Instructions

1. Peel the potatoes and slice them into 1/4" round slices with a Mandolin.
2. Finely chop the onion and garlic.
3. Melt the butter over medium heat in a pan.  Add in the onion and garlic and cook until the onions are translucent.
4. Add the flour to the pan and stir and until combined.
5. Pour in the milk and cook, stirring occasionally, until the mixture thickens.
6. Stir in 2 1/2 cups of the shredded cheese and stir until mixed. (Save the other 1/2 cup for the top of the casserole.)
7. Spray a 9x13" baking pan with cooking spray.
8. Add a single layer of potatoes in the pan.
9. Salt & Pepper to taste.
10. Add a layer of the cheese sauce.
11. Repeat this process until you have three layers of potatoes and cheese sauce.
12. Cover the pan with aluminum foil and bake in an oven pre-heated to 400 degrees for 60 minutes.
13. Remove the foil at the 60 minute mark.
14. Continue to cook for 30 more minutes.
15. At the 80 minute mark, open the oven and sprinkle the remaining 1/2 cup of cheese on the top of the casserole. Cook 10 more minutes.
16. Allow to rest for 10-15 minutes before serving.