Heat the oil and butter in a small pot.
Add in the finely diced onions and cook til soft. Stir in the minced garlic and cook for an extra couple of minutes.
Add in the cream, nutmeg, salt and pepper. Bring to a low simmer and keep on the heat for 5 minutes to let the cream thicken.
Take off of the heat and stir in the parmesan. Set to one side.
Preheat the air fryer to 360F.
Peel the potatoes and slice finely with a knife or mandolin.
Layer the sliced potatoes in a small casserole dish and pour the cream mixture over the top to coat. Wrap the dish securely in foil.
Cook in the air fryer for 30 to 35 minutes until the potato slices are tender. Take care when removing the foil as there will be hot steam. Depending on how thickly you sliced the potatoes the timings may vary.
Once the potatoes are tender, remove from the air fryer and pre heat the broiler.
Sprinkle the remaining parmesan cheese and panko breadcrumbs on top and broil til golden brown.