I adapted this recipe from the "Creamy Au Gratin Potatoes" recipe on allrecipes.com. It turned out very tasty and I love the fact that it is a "from scratch" recipe without processed ingredients. Though it takes a little more time to make than a boxed au gratin potato mix, it is definitely worth it.
Au Gratin Potatoes
4 large russet potatoes
1 1/2 cups chopped onions
1 1/2 tablespoons butter
1 1/2 teaspoons minced garlic
fresh ground pepper
4 1/2 tablespoons butter
4 1/2 tablespoons flour
3/4 teaspoon salt
3 cups milk (whole milk is best for a creamy sauce)
2 1/4 cups shredded sharp white cheddar
3/8 cup grated Parmesan cheese (a little less than 1/2 cup)
1/8 teaspoon cayenne pepper
1/2 cup bread crumbs
3 tablespoons melted butter
Preheat oven to 375 degrees. Grease a 3 quart casserole dish or a 9x13 baking pan.
Peel potatoes and slice into 1/4" slices or cut the potatoes into quarters lengthwise then cut long potato quarters into 1/4" pieces so that you end up with triangular potato pieces (I like to cut it this way for texture, but the picture above is from a time that I just sliced the potatoes). Place the potatoes in a pot with enough water to cover and bring to a boil; boil for about 8 minutes. Drain and set aside.
In a skillet melt 1 1/2 tablespoons of butter. Add chopped onion and saute until soft. Add garlic and cook for 1 minute. Place onion/garlic mixture in a bowl to cool and set aside.
In a saucepan melt 4 1/2 tablespoons butter. Add flour, salt , and cayenne pepper; cook, whisking, for 1 minute. Whisk in milk slowly. Cook, stirring constantly, until mixture has thickened and come to a boil. Add shredded cheese and parmesan and cook for about 30 to 60 seconds, stirring until cheese melts. Remove from heat.
Place half of the potato pieces on the bottom of the greased casserole dish. Sprinkle with half of the onion/garlic mixture and pour over a little less than half of the cheese sauce. Layer the remaining potatoes,then onions/garlic mixture and then top with the remaining cheese sauce, spreading cheese sauce so that it covers all of the potatoes. Cover with foil that has been sprayed with non-stick spray and bake for 1 hour and 30 minutes.
While potato casserole is baking combine bread crumbs and 3 tablespoons butter and stir with a fork until well combined. After casserole has baked for 1 hour and 30 minutes remove and sprinkle bread crumbs evenly over casserole. Bake for 5 more minutes or until browned on top.