For this you will need:
1. Whisk the egg, mustard and salt together in a small bowl.
2. Continue to whisk as you begin to add 1 c. oil drop by drop.
3. As the mixture begins to thicken, add the oil a little more quickly, ending in a thin, steady stream.Whisk in the vinegar.
5. Squeeze the mayonnaise onto the egg.
It's easy :)