Preheat the oven to 180°C (360°F).
To a blender, add the cashews, plant-based milk, water, olive oil, nutritional yeast, stock powder, garlic powder, dried thyme, dried rosemary, salt, and pepper. Blitz thoroughly until the mix is completely smooth. It might look quite thin at first, but it'll thicken in the oven as it bakes together with the starchy sliced potatoes.
In a greased oven dish, arrange approx. one third of the raw potato slices to create layers. Pour over approx. one third of the blended cream mix and sprinkle with approx. one third of the chives. Repeat this process until you have used up all of the potato slices. If you have any potato ends or odd pieces, add all these in the first layer.
Press down on the potato slices using the back of a spoon – the creamy mix should come to just below the top layer of potato. If necessary, pour over a little more plant-based milk.
If using plant-based butter, dot small amounts of this all over the surface of the potatoes. Cover the dish with tin foil and bake in the oven for approx. 45 minutes.
After 45 minutes, remove the foil and continue to bake for another 15-20 minutes or until the potatoes are tender enough to easily pierce with a knife or fork. The cooking time may vary slightly depending on how thinly you sliced the potatoes.
To make the top extra golden and crispy, you can place the dish under the grill for an additional 5-10 minutes (although it should already be a nice golden-brown colour after baking with the foil off).
Once cooked, remove the dish from the oven and leave it to sit for 5 minutes before serving. This allows the creamy mix to thicken and set in the potato.