Said it before; saying it again: There is no such thing as too much cheese.
- 1⁄2 cup butter
- 1⁄2 cup flour
- 3 cup milk
- 1 tbsp. Dijon mustard
- 1⁄2 tsp. salt
- 10 cups thin sliced Yukon gold potatoes, about 3 lbs.
- 1 1⁄2 cup shredded Gruyere (6 oz.)
- 1 1⁄2 cup shredded Cheddar cheese (6 oz.)
Heat oven to 350°. Grease 13 x 9 inch glass baking dish with cooking spray.
In a 2‑quart saucepan, melt butter over medium heat. Stir in flour with wire whisk until smooth. Gradually stir in milk. Heat to boiling; reduce heat to low cook about 5 minutes stirring frequently, until sauce is slightly thickened. Stir in salt and mustard.
Place half the potatoes in baking dish; top with half the sauce and half of each of the cheeses. Repeat layers.
Bake 50–55 minutes or until potatoes are tender and top is golden brown. Let stand for 5–10 minutes before serving.
High altitude: slice potatoes 1⁄8 inch thick and bake 1 hour to 1 hour and 5 minutes.