Boil 1360g of small yellow waxy potatoes in lightly salted water, skins on, until tender. Drain and, when cool enough to handle, peel and slice ¼in / 5mm thick into a large bowl.
In a saucepan, combine 1 medium chopped yellow onion, 1½ cups of water, 4 teaspoons of beef bouillon granules, and ½ cup of white vinegar.
Add ¾ tablespoon of salt, ½ teaspoon of ground white pepper, 1 teaspoon of sugar, and 2 teaspoons of mild German mustard. Bring to a boil and pour over the potatoes.
Let stand for at least 1 hour. Gently stir in ⅓ cup of neutral oil, adjust the seasoning, and serve at room temperature.
