Pour the double cream and milk into a large pan. Stir in the thyme, garlic, nutmeg and miso paste, if using, then season. Bring to a gentle simmer, then add the potatoes. Cook for 10-15 mins or until the potatoes are just tender, then remove from the heat.

Butter a 15cm wide, high-sided dish that is air fryer safe. Heat the air fryer to 180C. Spoon a third of the potato mix into the dish, spread out evenly, then top with a third of the brie. Repeat with the remaining potatoes and brie, finishing with a layer of brie on top. Cover with foil.

Cook in the air fryer for 50 mins-1 hr, removing the foil for the final 10 mins. You may need to test the centre of the gratin with a sharp knife – if it goes through without any resistance, it's ready to eat. Carefully remove from the air-fryer and leave to cool for 10 mins before serving.