Preheat an oven to 180°C Thinly slice the peeled potatoes by hand or using a mandoline, (about 2-3mm, ensuring they are as even as possible as this will help them to cook at the same time) and wash potatoes well in cold water.
Grease the surface of a round or oval baking dish with soft butter and then rub with sliced garlic. Leave the garlic scattered in the dish.
Combine the milk, cream and wasabi paste and season well.
Arrange the sliced and washed potatoes in a single layer around the baking dish and then pour over the cream and milk mixture.
Place into a preheated oven for 20 minutes until nicely browned on top and the potatoes are cooked, the cream and milk reduced until thick and creamy.