Another great recipe from Epicurious. I replaced the blue cheese with gruyere because one of my guests was not a blue cheese fan. I think that the blue cheese version would be delicious with roast beef, so I'll try it that way next time.
I've also changed the cooking time as well. The original recipe called for 90 minutes of cooking, and that is simply not long enough.
• 3/4 cup (packed) grated extra-sharp cheddar cheese (about 4 ounces)
• 3/4 cup crumbled Danish blue cheese (about 4 ounces)
• 1/3 cup (packed) freshly grated Parmesan (about 1 1/4 ounces)
• 4 pounds russet potatoes, peeled, cut into 1/4-inch-thick rounds
• 1 1/2 teaspoons salt
• 1/2 teaspoon ground black pepper
• 1/4 cup finely chopped onion
• 3 tablespoons all purpose flour
• 4 tablespoons (1/2 stick) butter
• 3 cups whole milk
Preheat oven to 400°F. Lightly butter 13x9x2-inch glass baking dish. Mix cheddar cheese, blue cheese and Parmesan in small bowl.
Arrange half of potatoes in prepared baking dish, overlapping slightly. Sprinkle with teaspoon salt and 1/4 teaspoon pepper. Sprinkle onion over, then flour. Dot with 2 tablespoons butter. Sprinkle half of cheese mixture over. Top with remaining potatoes, 3/4 teaspoon salt, 1/4 teaspoon pepper and 2 tablespoons butter. Reserve remaining cheese.
Bring milk to simmer in medium saucepan. Pour milk over potatoes (milk will not cover potatoes completely). Cover baking dish tightly with foil. Bake 45 minutes. Uncover dish (liquids in dish may look curdled); sprinkle potatoes with reserved cheese mixture. Reduce heat to 350 and bake uncovered until potatoes are tender and cheese is deep golden brown, about 1 1/2 hours longer or until liquid has been absorbed. (Can be prepared 2 hours ahead. Let stand at room temperature. Cover and rewarm in 375°F oven about 20 minutes.) Remove from oven; let stand 15 minutes before serving.