Bring a large pot of salted water to a boil. Add potatoes and cook until tender but still firm, about 10 minutes. Drain and set aside. Place eggs in a saucepan and cover with cold water. Bring water to a boil and immediately remove from heat. Cover and let eggs stand in hot water for 10 to 12 min. Remove eggs from hot water, cool, peel and chop. In a large bowl, whisk together the mayonnaise, mustard, turmeric and onion. Add the still-warm potatoes and stir until evenly coated. Gently mix in the hard-cooked eggs. Serve immediately, or refrigerate and serve cold.