The quintessential French potato gratin from the Dauphiné region: thinly sliced firm potatoes baked slowly in garlic-infused double cream and milk until meltingly tender and creamy, with a natural golden crust.
Slice potatoes 3mm thin on a mandoline. Do NOT rinse in water, as natural starches are essential to bind the cream.
Rub a ceramic baking dish with cut garlic clove and butter. In a saucepan, warm cream, milk, remaining minced garlic, nutmeg, salt, and pepper until steaming.
Arrange sliced potatoes in neat overlapping layers in the dish. Pour the warm garlic cream over until potatoes are just barely submerged.
Dot with knobs of butter. Bake at 160°C for 1 hour to 1 hour 15 minutes until potatoes are meltingly tender when pierced with a knife and top has a deep golden caramelized crust.