Preparation

• 1 Pre-heat oven to 350°F.2 Butter a 2" deep hotel pan (12"x 20"). Slice potatoes 1/8" - 1/4" thick. Place in large pot, cover with cold water, bring to boil and simmer until barely tender, 7 - 10 minutes.3 Alternately, blanch by steaming until barely tender. Air-cool potatoes spread out on sheet pan, 10 - 15 minutes.4 Meanwhile, sweat leeks in butter until softened, about 7 minutes. Have mustard sauce ready.5 To assemble gratin, layer 1/4 of potatoes, 1/4 of sauce, 1/4 of leeks, 1/4 of cheese in hotel pan.6 Repeat this process to create 4 layers. Cover tightly with foil. Bake for 35 - 45 minutes to an internal temperature of 175°F.
• Source: Idaho Potato Commission