Step 1In a heavy mortar and pestle, crush the garlic to a paste with the salt. Stir in the egg yolk, and mix until smooth.
Step 2Put the olive oil in a beaker or something with a spout. Stirring, always in one direction, add olive oil drop by drop until the aioli begins to thicken and emulsify. At this point, you can begin adding the olive oil in a very thin stream, stirring constantly until very thick.
Step 3Taste and adjust seasoning. If desired, for example, if serving it with steamed artichokes, add a teaspoon or so of fresh lemon juice to taste.