Mix the milk, oil, cornstarch, egg and salt well with the whisk. Let the whole thing boil once (briefly boil) while whipping vigorously. Now let the mixture cool down and stir it from time to time.
Season the cold mayonnaise with vinegar and, if you like, with mustard and / or sugar.
Tip:
This cooked mayonnaise is also very suitable for stretching purchased mayonnaise, for example.
The portion size is roughly equivalent to a glass of mayonnaise.