Peel and slice the potatoes very thin, either using a mandonline or food processor.
Smash the garlic cloves, add a dash of kosher salt, and chop until you have a creamy garlic paste.
Add the potatoes, garlic, scallions, half & half and butter to a heavy saucepan. Season with the nutmeg, salt and pepper.
Simmer for 15-20 minutes until the potatoes feel tender.
Taste again for seasoning.
Pour into the baking dish, add the grated cheese (can be made one day ahead to this point. If making ahead, allow the potatoes to cool, cover with foil and store in the refrigerator. Make sure to bring them to room temperature before baking) bake with foil on for 30 minutes (or until bubbling). Take the foil off and bake for 10-15 minutes until golden brown. Let rest for 15 minutes before slicing.
Recipe by Cook Eat Run at https://cookeatrun.com/2013/11/18/potatoes-au-gratin/