1. Tear off two fairly large sheets of aluminum foil (approx. 36" each), and lay one horizontally with the other one on top going vertically.
  2. Spray both sheets very well with cooking spray.
  3. Place half of the sliced potatoes in the center of the two sheets of foil.
  4. Put half of the sliced onions on top of the potatoes.
  5. Drizzle olive oil over the potatoes and onions, and dot with little pieces of margarine.
  6. Sprinkle salt and pepper to taste.
  7. Make a second layer by repeating the above directions.
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