About 1 quart of peeled and thinly sliced potatoes
3 cups milk
? cup butter
? cup flour
1 onion sliced
Put potatoes and onion in the crockpot.
In a saucepan put the butter and flour.  Cook for a few minutes to take away the raw taste of the flour.  
Add milk gradually and cook for a few minutes on low.  This sauce will begin to thicken.
You can add some cheese here if you would like.
Pour sauce over potatoes and cook on low for about 3-4 hours.
Dee-licious!