Add the egg, lemon juice, vinegar, mustard, & salt to the jar that came with your immersion blender.
Slowly pour the oil on top and let it settle for a minute.
Wait until there is clear separation between the egg mixture & the oil - you do not want them to mix. If this hasn't happened yet, wait until it does.
Place your stick blender in the jar & press it firmly to the bottom, making sure it's covering the egg yolk.
Turn it on & keep it pressed against the bottom of the jar for at least 10 to 15 seconds, without moving it.
Once the mayonnaise starts to emulsify & thicken, slowly move the stick blender up & down to fully combine the ingredients.
Stir the mayonnaise, adjust seasoning to taste & place in an airtight storage container in the refrigerator.
