Rick Rodgers, Epicurious.com
3/4 cup (packed) grated Extra-Sharp Cheddar cheese (about 4 ounces)
3/4 cup crumbled Danish Blue cheese
1/3 cup (packed) freshly grated Parmesan (about 1 1/4 ounces)
4 pounds russet potatoes, peeled and 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 degrees. Lightly butter a 13 x 9 x 2 glass baking dish. Mix Cheddar, Danish Blue, and Parmesan cheeses in a small bowl.
Arrange half of the potatoes in prepared baking dish, overlapping slightly. Sprinkle with half of the salt and pepper. Sprinkle onion, then flour. Dot with 2 tablespoons butter. Sprinkle half of the cheese mixture over. Top with remaining potatoes, salt, pepper and butter. Reserve the remaining cheese.
Bring milk to a simmer in a 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. Bake uncovered until potatoes are tender and cheese is deep golden brown, about 45 minutes longer. Remove from oven; let stand 15 minutes before serving. (Can be prepared 2 hours ahead. Let stand at room temperature. Cover and re-warm in 375 degree oven for about 20 minutes.)