Put the whole egg with mustard, oil and salt in a container and mix with the hand blender to a spreadable mass (only takes a few seconds). Now just add pepper and lemon juice to taste.
Always works and tastes good with salads or, for example, with tuna, parsley and capers as a spread. Keeps in a cool place for approx. 24 hours.
Tip: If the mayonnaise is too runny, just add a little more oil.