Ensure your egg is at room temperature (crucial for emulsion).

Place egg in the bottom of a clean mason jar.

Add salt, lemon juice, and mustard (if using).

Pour avocado oil over other ingredients.

Place immersion blender at the bottom of the jar, completely submerging it in the mixture.

Without moving the blender, turn it on and hold it at the bottom until you see mayonnaise forming.

Once mixture begins to emulsify and turn white, slowly move the blender up and down until all oil is incorporated.

Blend until desired consistency is reached (about 30 seconds total).