Potatoes Au Gratin

We largely celebrate Passover in my house, but some of us celebrate Easter, which often falls within the confines of the week of Passover.  The traditional Easter dinner for us (and many others) is a ham, which I would ordinarily serve macaroni and cheese for, but not when wheat products are off the table.  I could make a farfel dish to substitute, but this is another option (using matzah cake flour for the flour, or gluten free flour if you are working with some gluten restrictions in your guests).  This is essentially the sauce I make for my macaroni and cheese, but poured over potatoes.  I stood the potatoes up in the pan, but you could layer them.

• 4 russet potatoes, sliced into 1/4 inch slices
• 1 onion, sliced into rings
• salt and pepper to taste
• 3 tablespoons butter
• 3 tablespoons all-purpose flour
• 1/2 teaspoon salt
• 2 cups milk
• 1 1/2 cups shredded Cheddar cheese
• salt and pepper to taste

1. Preheat oven to 400°F (200 degrees C).
2. Butter an 8x8 casserole dish.
3. Arrange the potatoes and onions in the prepared baking dish, staggering potato and then onion.
4. Season with salt and pepper to taste.
5. In a medium-size saucepan, melt butter over medium heat. Mix in the flour and salt, and stir constantly with a whisk for one minute. Stir in milk. Cook until mixture has thickened. 
6. Stir in cheese all at once, and continue stirring until melted and smooth, about 30 to 60 seconds. 
7. Pour cheese over the potatoes, and cover the dish with aluminum foil.
8. Bake 1 1/2 hours (90min.) in the preheated oven.
9. For a crisp topping, change the oven setting to broil for 5 minutes before removing the dish.