Peel and wash the potatoes. 

Mix the water and the powdered milk, add the cream with the butter, garlic, salt/pepper/nutmeg, then bring to the boil. 

Cut the potatoes into round slices, add them to the first warm mix and stir occasionally. 

Cook on medium heat. As soon as the liquid thickens, place the potatoes onto a baking sheet and cover with the liquid. 

Sprinkle with grated cheese and bake in the oven at 375°F (190°C) for 30 mins. 

You can prepare the gratin the day before. The following day, sprinkle on grated cheese and brown in a hot oven.