A mixture of sumac, sesame seeds, hyssop and whatever else is lying around, za'atar is the condiment of choice all around the Middle East.
Sprinkled on like mixed herbs, it goes with pretty much everything, but it's at its best on bready things, be it on a slice of soft white bread with hummus, or mixed with olive oil on a toasted pita, or on a pizza.
One of the more peculiar things about za'atar is that every blend seems to be quite different; some miss out the hyssop, some the sumac. And all of the other ingredients seem to have been gathered by a chef running his hand down a used kitchen worksurface, and are totally variable.
The ingredients of the blend I have here are:
Hyssop, Sesame seeds, Wheat, Parsley, Chickpeas, Salt, Citric acid, Soya oil.