Preheat the oven to 200 degrees Celsius or the air fryer to 190 degrees Celsius.
Slice the potatoes into thin slices, preferably using a mandolin. Add to a big bowl.
Drizzle with olive oil, add sea salt, thyme and garlic (if using). Mix thoroughly.
Divide potato slices between muffins tins. Drizzle with more olive oil on top (optional).
Cover with aluminium foil and place in the oven/air fryer. Bake for 20-25 minutes the oven or 15-20 minutes in the air fryer. Remove the foil and bake for another 20-25 minutes in the oven or 15-20 minutes in the air fryer, until the potatoes are golden brown and soft.
Remove from the oven, run a knife around the edges to release the potato stacks. Serve immediately.