Preheat the oven to 200°C or the air fryer to 190°C.
Slice the potatoes into thin slices (about 2mm), using a mandolin or food processor and add to a big bowl.
Drizzle with olive oil, add sea salt, thyme, stock and garlic and mix thoroughly.
Lightly oil the muffin tray.
Divide potato slices between muffins tins, layering the slices about 1cm above the rim as they'll sink when baked. Drizzle with a little more olive oil on top.
Cover with aluminium foil and place in the oven. Bake for 20-25 minutes in the oven. Remove the foil and bake for another 20-25 minutes, until the potatoes are golden brown and soft.
If using an air fryer, cook for 15-20 minutes, remove the foil and cook for another 15-20 minutes.
Remove from the oven and run a knife around the edges to release the potato stacks.