Add egg, lemon juice, mustard, salt and pepper to blender and blend for one minute until light and frothy.

Remove fill cap and, while blender is running, slowly begin pouring oil into blender in a very thin stream. This step should take at least a minute, but you may need to stop and scrape down sides of blender.

Once all oil is incorporated, turn off blender and taste the mayo. If it's missing something, stir it in at this time. Otherwise, transfer to a glass container and store in fridge up to one week.