4 cups thinly sliced potatoes (I used russet, unpeeled, very thinly sliced) 3 tablespoons butter 3 slightly heaping tablespoons flour 1 1/2 cups milk 1 teaspoon salt (I used garlic salt) 2 cups grated sharp cheddar cheese 1 onion, sliced
In a small sauce pan, melt butter and blend in flour. Let sit for a minute. Add all of cold milk, stirring with a whisk. Season with salt. Cook sauce on low until smooth and boiling, stirring occasionally with a whisk. Reduce heat and stir in cheese. Continue to cook until melted.
Place a half of the sliced potatoes and 1/2 the sliced onions in a lightly greased one quart casserole dish. Pour half of cheese sauce over potatoes. Repeat with second layer of potatoes, onions and cheese sauce. Sprinkle the remaining cheese on top.