Potatoes with Mayonnaise

2 lb potatoes
1 onion, large
2 tsp sugar
1 tsp salt
1 tbsp white vinegar
2 cup water
1 lb sour cream
3 tbsp mayonnaise
1 tsp mustard
1 tbsp lemon juice, fresh
1 tbsp sugar
1/2 tsp salt

Cook potatoes in their skin. Do not over cook! Peel them after cooking, slice them. Make marinade with salt, sugar, vinegar, onion and as much water as needed to cover the sliced potatoes. Let it stand over night in the marinade. Strain the marinade from the potatoes make the dressing with these ingredients: sour cream, mayonnaise, sugar, lemon juice, salt, mustard. Pour over the marinated strained potatoes. Let it stand for a few hours before serving.