I love the aniseed flavor of celeriac. If you’re not a huge fan of aniseed, just omit the celeriac and use all potato. You can also grate some Gruyère or Fontina cheese in between the layers.
Preheat the oven to 350 degrees.
Grease a baking dish with butter and sprinkle the crushed garlic on the bottom of the dish.
Drop the sliced potatoes and celeriac into a saucepan of boiling water for 4–5 minutes, then drain and make layers in the dish, overlapping the slices a little and seasoning each layer.
Pour the half and half over the potatoes and use your hand to push down the potatoes until they are completely immersed in the milk. Sprinkle the nutmeg over the potatoes and cover with a butter wrapper or parchment paper.
Bake in the oven for 30 minutes. Remove the butter wrapper and turn up the heat to 400 degrees until the top is golden (about 20 minutes).