In the bottom of a tall mason jar add the egg, salt, pepper, mustard, and lemon juice.
Carefully add in the avocado oil.
Place your immersion blender into the very bottom of the jar where the egg is. Then turn on your blender to high and blend only the egg at the very bottom. When you see it turn creamy slowly move your immersion blender up and down to slowly incorporate the avocado oil.
Once all of the oil has been combined remove your immersion blender and scrape off the excess. Put a lid on the jar and store in the fridge for up to a week.