To a blender or a food processor, add your egg yolk, egg, vinegar, mustard, garlic, and salt.
Blend this mixture well until super smooth and there are no large pieces of garlic left.
Keep the blender or processor on, then very slowly begin to add your oil. We are essentially making a mayonnaise here, slowly emulsifying the oil into our mixture.
Once the mixture begins to thicken up, you can add the oil more quickly.
Once fully emulsified, remove about half the mayonnaise mixture from the blender.
Add in your cilantro and blend on high until the cilantro breaks down into very small pieces and the sauce appears green.
Add back in the rest of your mayo mixture and blend until fully emulsified.
Pop into a squeeze bottle and enjoy!