Pre-heat oven to 350° (180° celsius). Lightly butter an 8x6 inch (21x16 centimeter) baking dish.
Peel and thinly slice the potatoes.
Grate the Fontina (if you can't find Fontina, Gruyere or Gouda can be substituted).
In a medium pot melt butter, whisk in flour, whisk until smooth, add milk and continue whisking add salt and pepper and continue whisking until thickened (just until bubbles start to appear) remove from heat. (If too thick add a little milk).
In lightly buttered baking dish add a layer of potatoes (1/3 of the potatoes), sprinkle with half the grated cheese and 1/3 of the white sauce, another layer of potatoes, last half grated cheese, 1/3 white sauce, last layer of potatoes, white sauce and sprinkle with the freshly grated Parmesan cheese. Bake covered for 45 minutes, uncover and continue cooking for approximately 30 minutes. Let sit 5-10 minutes before serving. Enjoy!