Potato and Onion Casserole

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  1. Bring a large pot of salted water to a boil.
  2. Add potatoes and cook until tender but fi rm.
  3. Drain.
  4. Preheat oven to 300 degrees.
  5. In another pan, combine mustard, fl our, milk, salt, and soup. Mix well and heat until thickened.
  6. Starting with potatoes, arrange potatoes, tuna, and onions in alternating layers in a 9x13-inch baking dish. Pour the mustard sauce over the top.
  7. Bake in a preheated oven for 1 hour or until bubbly
  8. Optional: sprinkle a layer of cheddar or mozzarella cheese over the top.