The tale has it that this layered potato and onion dish originated with French homemakers who didn't have a home oven. They would take it to the boulangerie (the bakery) on Sunday morning on their way to church, and pick it up on the way back home for Sunday dinner.
Wash the potatoes and slice them thinly with a sharp knife, mandoline, or food processor. Cut the onion in half lengthwise, then in thin slices across.
Butter a baking dish. Make layers of the potatoes and onions. Top each layer with thyme leaves, salt, and pepper. Finish with a layer of potatoes in an overlapping pattern.
Pour the chicken or vegetable stock over, then cut the butter into small pieces and place them evenly on top of the last potato layer. Cover and bake for 1 hour or until the potatoes are soft all the way through.
Uncover, raise the heat to 425°F and bake until the potato slices on top are golden brown.
Keyword potato casserole, potatoes, potatoes and onions