In a large bowl, toss together the cabbage, carrots and onion and set aside.
To make the mayonnaise, place the egg yolks, mustard powder and vinegar in a food processor and blend. While the motor is running, drizzle the oil very slowly through the lid, incorporating each drop before adding more. Continue adding the oil until the mayonnaise reached the desired consistency, adding a little warm water if it becomes too thick. Add more mustard powder or vinegar to taste and season with white pepper.
Stir half of the mayonnaise through the vegetables and mix together well. Cook's tips: Keep the remaining mayonnaise in a sterilised container in the fridge for up to 3 days. For something different, add a handful of raisins and walnuts to the mayonnaise, or sprinkle with poppy seeds.
*This recipe contains raw eggs. Public health advice is to avoid consumption of raw or lightly cooked eggs, especially for those vulnerable to infection, including pregnant women, babies and the elderly.