Place 1 egg in a blender
Add 1/2 teaspoon of salt
Place 1 pinch of white or black pepper
Put 1 tablespoon of mustard
Add 3 tablespoons of lemon and blend everything very well.
Once the ingredients are well integrated, you will integrate the oil little by little while the blender is still working.
It is very important that you add the oil slowly. That's the key to thickening the mayonnaise.