In a mini food processor or with an electric mixer or mortar and pestle crush and mix garlic, salt and egg yolk.

While mixing continuously start to add the oil very gradually a few drops at a time as for mayonnaise. It will become very thick. At the end add the lemon juice and maybe some extra salt.
* Making aioli with 1 egg yolk can be a a little tricky due to the ability to keep the small volume of egg yolk mixing while adding the oil without the aioli splitting.
The reason I have the recipe as such is purely because it makes a manageable quantity whereas twice as much is more difficult to use up.