Peel and thinly slice potatoes and onions. Set aside. In large saucepan, bring water and margarine to boil. Reduce heat to low. Layer 1/3 of potatoes, 1/3 of onions, and 1/3 of popcorn salt. Repeat layers two more times. Sprinkle pepper or Cajun seasoning on top. Cover and simmer on low heat 15 to 20 minutes until potatoes are tender.
Cajun Country -- New Iberia, Louisiana