Preheat oven to 180ºC. Slice the potatoes into thin slices (1/8 inch thick) and rinse in cold water. Drain and dry using a towel. Put the potatoes in a pan and cover with milk. Add salt. Bring to a boil starting at moderate heat for 5 minutes then low heat for 10 minutes. Stir from time to time.
Rub a fireproof dish with garlic and grease it well with butter. Transfer half of the potatoes in the gratin dish, add half the cheese, half the cream and pepper to the layer. Put the second half of the potatoes and cover with the rest of cheese and cream. Put the dish in the oven and cook for 1 hour at 180ºC. Gratin Dauphinois is ready when the top is golden and brown.