Pick 6-8 similar yams in size. I try to pick longer more slender ones. Clean and then place in cooking pot with salted water to completely cover. Heat to a boil then reduce to a simmer. Cook for 20-30 minutes until begin to get tender. Cover and let rest until water is just warm. Drain water, peal away the skin and then cut into 1 1/2" round pieces. Heat oven to 350 degrees. Layer sliced pineapple on bottom of 9x13" pan. Add yams. Cream butter, brown sugar, flour, cinnamon and salt. Add walnuts. This makes a pralines type topping. Spread over yams. Bake 45 minutes at 350 degrees. Add marshmallows for last 15-20 minutes. Per Serving (excluding unknown items): 334 Calories; 21g Fat (55.8% calories from fat); 2g Protein; 36g Carbohydrate; 3g Dietary Fiber; 37mg Cholesterol; 363mg Sodium. Exchanges: 1 Grain(Starch); 0 Lean Meat; 1/2 Fruit; 4 Fat; 1 Other Carbohydrates.