Au Gratin Potatoes

We had these Au Gratin Potatoes from the $5 Dinner Mom with our Christmas Eve ham. Visit $5 Dinners for your chance to win a copy of her new cookbook--she's giving away 10 copies a day for two weeks!

6 large Russet potatoes, peeled and thinly sliced
1 yellow onion, thinly sliced
1 teaspoon garlic powder
1 teaspoon each of salt and pepper
4 tablespoons butter or margarine
4 tablespoons flour
4 cups milk
2 cups sharp cheddar cheese

1. Preheat oven to 350°. Grease a 9x13-inch glass baking dish.
2. Place a layer of thinly sliced potatoes, followed by a layer of thinly sliced onions, and finally topped with another layer of thinly sliced potatoes in the glass baking dish. Sprinkle with garlic powder, salt and pepper.
3. In a medium saucepan, melt the butter and quickly whisk in the flour to form a paste. Pour the milk into the saucepan, whisking as you pour. Whisk until butter/flour paste dissolves into the milk.
Heat the sauce over medium-high heat for 4 to 5 minutes, until it begins to bubble and thicken. Once thickened and bubbling, pour the sauce over the potatoes and onions in the glass baking dish.
4. Sprinkle shredded sharp cheddar cheese over the potatoes and sauce. Cover with foil and bake in the preheated oven for 35 minutes. Remove foil and return to the oven and bake for another 15 to 20 minutes, or until cheese is golden on top and sauce is bubbly.