This will make enough for a 9X13 pan. Be smart and buy the disposable pans for this. Saves the cleanup in the kitchen and you won't lose a pan. Our church kitchen is full of orphaned casserole dishes. If we opened a store and sold all the lost kitchen casserole dishes we could probably cover the church budget for an entire year.
preheat oven to 350 degrees
1 cup chopped onion (2 medium)
2 cloves garlic minced
4 Tablespoons butter
4 Tablespoons flour
dash of salt and pepper
2 1/2 cups of milk
1 1/2 cups shredded cheddar cheese
2 pounds of potatoes (6 medium sized potatoes)
grease a 9X13 inch pan or spray with cooking spray
make the sauce:
cook the onion and garlic in the butter in a sauce pan until it's tender but not brown. Stir in the flour and salt and pepper. Add the milk all at once. Cook and stir over medium heat until thick and bubly. Add half of the cheese until it is melted.
While sauce is cooking, peel and thinly slice the potatoes. Place half the potatoes in the pan. Cover with half the sauce. Repeat with the rest of the potatoes and the rest of the sauce. Finish off the top with the other half of the cheese. And maybe some panko bread crumbs if you have them. This gives it an extra touch of texture.
Bake covered for about 40 minutes. Then uncover and bake for another 30 minutes or so until the potatoes are tender.
Don't get all scientist over these measurements and times. Sometimes it's ready sooner. Sometimes later. It's supposed to make enough for 8-12 people, depending on how hungry they are or how many other choices they have.
You could also include a few slices of crumbled cooked bacon. I find it easier to cut the bacon into very fine pieces and fry them in a small pan. They cook more evenly and you don't have to spend a lot of time crumbling stuff.