1cuphalf-n-half(this year I made it with 1/2 cup heavy cream and 1/2 cup half-n-half and it was even better! so I'll be making it that way from now on.)
Use a mandoline to thinly slice potatoes to 1/8 inch thick. Put into large bowl. Then grate gruyere cheese and set aside.
Add salt, black pepper to bowl and toss potatoes to coat as evenly as possible. Then add flour, thyme, garlic powder to the potatoes and toss again to distribute. Add 1/2 of cheese to potatoes and toss.
Butter a 7x10 baking dish and put half of potatoes into the dish, laying them flat. Add a little bit more cheese over the top of them. Then place remaining potatoes on top of the others, in a flat and organized manner. Sprinkle with remaining cheese.
Pour half-n-half over the potatoes, distributing evenly. Cover the top of the pan with aluminum foil and secure it tightly.
Bake for 30 minutes covered, then remove foil and bake for 20-30 more minutes more, until potatoes are cooked through, and can be pierced easily with a fork and everything is golden brown and bubbling.