Two Cheese Potato Gratin - cooking recipe

Ingredients

1/2 cup butter
1/2 cup flour
3 cups whole milk
1 tablespoon Dijon mustard
1/2 teaspoon salt
10 cups yukon gold potatoes, sliced 1/8-inch thick (approx. 3 lbs)
2 cups shredded gruyere cheese
2 cups shredded cheddar cheese

Preparation

Heat oven to 350 degrees.
In sauce pan melt butter.
Stir in flour & whisk until smooth.
Gradually stir in milk. Heat to boiling, then reduce heat to low & cook for 5 minutes, stirring frequently until thickened.
Stir in mustard & salt.
Coat a 9x13 casserole with cooking spray. Place 1/2 potatoes in pan slightly overlapping.
Top with 1/2 of the sauce & 1/2 of the cheeses.
Repeat layers.
Bake approximately 50-55 minutes or until golden & bubbly.
Let stand out of oven for 5-10 minutes before serving.