As Pierrette implied, I was making some toum this morning. This isn't the first time, and won't be the last. One of the shwarma places I go to regularly serves a garlic sauce with its shwarmas that is excellent, albeit incredibly strong, so I decided that I needed to learn how.
The first time I tried, I was able to find out that the sauce is called toum, and find a few contradictory recipes. Like many traditional recipes, there are lots of ways to make it, and very few precise instructions. Unfortunately, toum is also a bit of a pain; it's sort of like a garlic and oil emulsion, and so the oil has to be added a bit a time. Meanwhile, garlic is very difficult to macerate in mortar and pestle, although it is doable.
If you're going to try a food processor, make a big batch - a few cloves of garlic is just enough for the food processor to throw around, but not enough to really latch on to, so there's not enough to really kick-start the emulsion with a teaspoon of oil.
Some people add a little mustard powder to help emulsify, others add some egg white to increase the creamy whiteness. I've tried the mustard, but not the egg white. I think that next time I might start by using a garlic press on the garlic to get it smaller with limited effort.
We'll see; when I feel like I've mastered it, perhaps I'll post more tips.