For the Sauce-

1. Sauté the onions in a pan until they are just turning translucent. Be sure not to brown since they will continue to cook in the oven.
2. Add the garlic in and sauté for 1 more minute.
3. Set aside.
4. Make the roux by melting the butter in a sauce pan on medium temperature.
5. When butter has melted, whisk the flour in and whisk continuously for 1 minute.
6. Slowly pour the milk in, while whisking, making sure there are no lumps.
7. Simmer for 1-3 minutes, whisking frequently, until sauce is thick enough to coat a spoon.
8. Turn the heat off.
9. Stir in the onions and garlic, salt, pepper, and fresh thyme.
10. Add half of the cheese to the sauce and stir until melted.

For the Potatoes-

1. Using a mandoline or a sharp knife, slice the potatoes about 1 mm thick.
2. Place the potatoes in a large bowl.

Assembly & Cook-

1. Preheat oven to 400 degrees F.
2. Place the remaining cheese in the large bowl with the potatoes.
3. Pour the sauce over the potatoes and cheese and mix until potatoes are evenly coated.
4. Place potatoes into 3 rows in a 9″x13″ baking dish.
5. Pour any remaining sauce over the top of the potatoes
6. Cover with foil.
7. Bake for 30 minutes, uncover, bake for another 30 minutes or until the tops of the potatoes are brown and the sauce is bubbling.
8. Let cool, serve, and enjoy!!