01 -
Warm your oven to 375°F (190°C). Take out your nicest baking dish and grease it up lightly with butter or cooking spray.
02 -
In a large skillet over medium heat, melt the butter. Let the sliced onions cook slowly for about 15-20 minutes until they're soft and deep golden. Your kitchen will smell incredible!
03 -
As the onions cook, slice your potatoes thinly, no thicker than a coin. Toss them in a mixing bowl with the cream, thyme leaves, and a dash of salt and pepper.
04 -
Place half your potato mixture in the greased dish, then add a layer of golden onions. Repeat the process with the remaining potatoes and onions. Finish it off by sprinkling Gruyère cheese over everything.
05 -
Cover the dish loosely with foil and bake it for about 45 minutes. Then take off the foil and let it cook for another 15-20 minutes until the top is bubbly, golden, and slightly browned.