1. Crush the garlic cloves with the salt in a mortar or deep bowl until you have a smooth paste. Take out some of it as it may be too much; you can add it back later.
2. Add the egg yolk. Anchor the bowl down by tying a dishtowel around it tightly, if necessary.
3. Using a fork or whisk, add the oil to the egg and garlic mixture starting very slowly, drop by drop. I like to use a spout in an olive oil bottle to regulate the flow but you can also drip the oil in from a spoon. As the mayonnaise thickens continue to add the oil in a very thin stream. Continue until all the oil has been incorporated.
4. If it gets too thick you can dilute it slightly with a tablespoon of warm water – don’t add more oil, it will just get thicker. Taste, and add more of the garlic, if desired.
This recipe can easily be doubled, and you can make the aïoli in a food processor but the texture and taste is not as fine as hand-made.