Add all of the ingredients (with the oil last) into the jar that came with your stick blender.
Give the ingredients a minute to settle, with the oil separating on top.
Place your stick blender in the jar and press it firmly to the bottom. Turn it on and keep it pressed against the bottom of the jar for at least 10-15 seconds. Once the mayonnaise starts to emulsify and thicken, slowly move the stick blender up and down to fully combine the ingredients.
Once it's all blended, remove the stick blender. Give it a few stirs with a spoon and place in a storage container in the refrigerator. It will stay fresh for up to one week.
See all my notes and tips above, including this avocado oil brand I recommend.