In a large saucepan over medium heat, bring the potatoes, milk, and garlic to a gentle simmer. (Sous vide?)

Continue simmering the potatoes for 15 minutes, until they just start to turn tender. Be very careful not to overcook them as they need to hold their shape for layering in the pan.

Preheat the oven to 350 F.

Drain the milk from the pan and add the heavy cream, crème fraiche (or replace with the milk already used), salt, pepper, and nutmeg to the hot potatoes.

Heat the cream mixture to barely a simmer (a few bubbles are fine but no more) for 10 to 15 minutes until the potatoes are very tender, but not falling apart.

Butter a large baking dish and carefully lift the potatoes into the dish and layer without breaking them up too much.

Cover with the cream from the pan.

Sprinkle the Gruyere cheese over the potatoes.

Bake in the oven for 20 to 25 minutes, until the potatoes are golden brown on top and the cream soaked up.

This is a great make-ahead side dish. Simply refrigerate it for up to 1 day before the final baking stage. To reheat, bring it up to room temperature, cover with foil, and put it into a very hot oven as above.