Ingredients
1/2 block of unsalted vegan butter, melted
2 yellow onions, halved and very thinly sliced
Salt and freshly ground black pepper
3 pounds potatoes, scrubbed
3 fresh thyme sprigs
4 cups homemade veggie stock

Method
Add some salt to the sliced onions and cook them gently over medium heat until they are caramelized, about 30 to 40 minutes.
Turn on the oven to 250F
Use a mandolin to thinly slice the potatoes. Do not wash the potatoes after slicing, which allows them to keep starch and helps the dish come together.
The next step is to layer the dish. In the base of an oven-safe pan, spread a layer of the caramelized onions. Add a thin layer of sliced potatoes over the onions.
Drizzle some melted butter and veggie stock over the potato layer. Season with salt and pepper. Alternate the direction of the potato slices with each new layer to ensure an even arrangement. Continue layering potatoes, melted vegan butter, and veggie stock, seasoning each layer with salt and pepper as you go. After the last layer of potatoes, season again with salt and pepper, and sprinkle fresh thyme leaves over the top.
Make a cartouche. Cut a piece of greaseproof paper to fit the pan. Make a small hole in the center to allow steam to escape. Place the cartouche on top of the layered potatoes to help with even cooking and caramelization.
Cover the dish and bake in the oven at 250°F for about 1 hour to 1.5 hours.
After 45 minutes to 1 hour of cooking, remove the cartouche and lid.
Raise the oven temperature to 265°F to allow the veggie stock to reduce and the potatoes to caramelize on top. Bake for an additional 25 minutes or until the potatoes are golden and tender.

Allow to rest out of the oven for about 5 minutes before serving.