Put all the ingredients into a tall, narrow container. I used the one that came with my immersion blender. Follow this order: egg (be careful not to break the yolk), oil, white vinegar, salt, Dijon mustard.
Insert the immersion blender and push it all the way to the bottom of the jar.
Turn it on at the highest speed, and DO NOT move the blender for 10 seconds.
Almost instantly the mixture will begin to emulsify and look like mayo. Now you can move the immersion blender up and down to incorporate any oil sitting on the top.
Your homemade mayonnaise is ready. Place in a storage container in the refrigerator and use it within one week.
This recipe makes 1 cup of mayonnaise.
Nutrition facts: The nutrition facts provided below are estimates. 1 serving equals 1 tablespoon.