In a tall, narrow container, add neutral oil, one whole egg, lemon juice, garlic, and black truffle. Let the egg sit out for 30 minutes before use for better emulsification.

Using an immersion blender, blend on high speed for about 10 to 15 seconds until thickened to a mayonnaise-like consistency.

Taste and add salt as needed, then blend briefly again to mix the salt.

Serve immediately or store in an airtight container in the fridge for up to four days.