Peel and mince the garlic cloves.
Place the minced garlic into the mortar. Using the pestle, begin to pound the minced garlic until it is well-mashed.
Separate the egg yolk from the egg white. Incorporate the egg yolk and salt into the bowl with the mashed garlic. Stir well. Discard the egg white.
Very slowly, and adding only a little bit at a time, begin to incorporate the oil while mixing the garlic, egg yolk, and oil constantly. This is the step that requires patience! Be sure to go slowly so that the garlic and oil have a chance to blend well.
Once the mixture begins to thicken, incorporate the lemon juice. The resulting texture should be a creamy, smooth mayonnaise.
Refrigerate the mixture, which should last a few days.
Tip: If you do not have a mortar and pestle or are pressed for time, combine all ingredients in a small- or medium-sized bowl, and let the hand mixer do the work. Keep the hand mixer steady and pressed to the bottom of the bowl at first, and slowly let it come up to fluff the mixture as the mixture thickens.