4poundsrusset potatoes, peeled, cut into 1/4-inch-thick rounds
4tablespoons1/2 stick butter
1/4cupfinely chopped onion
2garlic cloves, minced
3tablespoonsall purpose flour
1 1/2teaspoonssalt
1/2teaspoonground black pepper
3cupswhole milk
Instructions
Preheat oven to 400°F. Lightly butter 13x9x2-inch glass baking dish.
In a small bowl, mix cheddar cheese, blue cheese and Parmesan; set aside.
Arrange half of potatoes in prepared baking dish, overlapping slightly.
In a large sauce pan over medium heat, melt butter. Add onions and garlic and saute until golden, about 6 minutes. Add flour, salt, pepper, and milk; cook until thickened. Add half of the cheese mixture, stir until combined.
Pour half of the milk mixture over the potatoes. Add remaining potatoes. Top with remaining milk mixture.
Cover baking dish tightly with foil. Bake 45 minutes. Uncover dish; 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.