In a small food processor (or a large one fitted with a small bowl), pulse the garlic and the egg white until you can’t see the garlic anymore.
With the food processor on, slowly begin to add the oil in order to start the emulsion. Make sure that the stream of oil going in is no more than a thin thread, or you risk the possibility of your sauce breaking.
Once all the oil has been added, add the lemon juice while the food processor is still running.
Season the sauce with a little salt and refrigerate until ready to use.

See more at http://www.antoniotahhan.com/2009/12/17/a-sauce-that-goes-with-everything/