Preheat your oven to 400 degrees F Oil a deep 9x13 baking dish Thinly slice 3 1/2 pounds potatoes and 1 small onion

Making the sauce

In a saucepan on medium heat, melt 3 tablespoons butter Add the sliced onion and 4 cloves of minced garlic Saute for 2-3 minutes until soft and translucent

Sprinkle 1/4 cup all purpose flour to coat the onions Slowly whisk in 1 cup chicken stock until the mixture has thickened Pour in 2 cups milk and whisk until fully combined

Stir in  1 tsp fresh thyme,  1 tsp salt,  and  1/2 tsp black pepper Remove the sauce from heat and set aside

Arrange the sliced potatoes in your oiled 9x13 baking dish Pour 1/2 of the sauce over the potatoes Sprinkle 1 cup shredded cheddar cheese and 1/4 cup freshly grated parmesan cheese over the top

Pour the remaining sauce over the cheese top with another 1/4 cup freshly grated parmesan cheese and another 1 cup shredded cheddar cheese Cover with foil and bake for 30 minutes  Remove the cover and bake for an additional 25 minutes until browned

Garnish if you desire and enjoy Click the link for full recipe and tutorial