Put all ingredients - except for the oil - in a tall container and mix everything well with a stick mixer (always do this by moving the stick up and down).
Then gradually add the oil in a thin stream, stirring continuously until the mayo has the desired consistency.
Personally, I prefer it a little more solid. It is important that all ingredients are at the same temperature, preferably at room temperature. Therefore, please take the egg out of the refrigerator in good time before preparing it.