Za'atar: The Levantine Spice Blend with Sumac and Sesame
Spices are something you buy in a store. That's my rule, and Israel can back it up with numbers: a bunch of wild oregano picked on a hillside used to earn you a court fine running into thousands of shekels, because the plant is a protected species and whole generations had been picking it faster than it could grow back. In this country, spices could land you in court.
Za'atar (Arabic: زعتر, Hebrew: זעתר) is a spice blend of dried Syrian oregano, tart sumac, toasted sesame seeds, and salt - a greenish-brown powder that, in Israeli cooking and across the whole Levant, you mix with olive oil and dip your bread in.

One Word for the Plant and the Blend
The word za'atar is confusing in two ways. First, it means both the herb and the finished blend, so at the market you have to ask what you're actually buying: green leaves, or the ground powder with sesame already in it. Second, the herb isn't thyme, whatever the English guidebooks call "wild thyme" - it's Syrian oregano, a sister of regular oregano. Even medieval scholars couldn't agree on the spelling: Maimonides wrote za'atar, while Obadiah of Bartenura, the Mishnah commentator, wrote tza'atar. The root of the word is Aramaic, which is why Hebrew and Arabic share it. Za'atar is the spice of the entire Levant: the same blend is mixed in Palestine, Lebanon, Syria, and Jordan, just in different proportions - the Nablus version sticks to the trio of herb, sesame, and sumac, the Lebanese one tends to be lighter thanks to thyme flowers, and the Aleppo one adds cumin, anise, and ground pistachios. Egyptian dukkah is a different blend altogether, coarser, made from nuts, coriander, and sesame without a single leaf of oregano. And in Turkish cooking, zahter in Hatay is a fresh herb salad with pomegranate molasses: a similar word, a different dish, a trap waiting just across the border.
The Hyssop of the Psalm and the Baker's Little Bag
The same plant has a different job in the Bible. The hyssop used at Passover to brush the lamb's blood onto the doorposts, and the hyssop the psalmist asks to be cleansed with, is according to botanists most likely Syrian oregano - a plant for purification, not for breakfast. Nobody can date when it became a blend with sumac and sesame; the oldest documented recipe for a flatbread with oil and za'atar comes from a tenth-century Arabic cookbook. What is modern is the label "Israeli spice": it shows up in the 1970s, and Palestinians resent it, because for them za'atar is the smell of home and the protected-plant law fell mostly on their foragers. The conservation authorities eventually announced that a handful for personal use would be allowed; and so the plant from the psalm went from being a crime to being a bureaucratic exemption.
What Holds the Blend Together
The oregano brings the aroma, warm and earthy, but without the other two characters it would be nothing more than dried herb dust. Sumac, the ground berries of the sumac shrub, brings the tartness that lemon provides elsewhere; toasted sesame adds fat and a nutty flavor, and salt glues it all together. The millers of Aleppo add the sesame only right before selling, because in the blend it quickly goes rancid and attracts moths - you can tell freshness by the smell, and packaged za'atar with no aroma is a bad souvenir, not a spice. Anyone who grew up in Czechia knows the idea from the simplest childhood meal: a slice of bread, butter, salt. Here the butter is olive oil and the salt is za'atar, except this salt also carries tartness and the scent of the hills.
It's eaten mostly in the morning. Zeit u za'atar, oil and za'atar, are two little bowls next to the bread: you dip a piece first in one, then in the other, and breakfast is over before the coffee is even ready. Bakeries make manakish, a flatbread spread with a paste of oil and za'atar, the blend gets sprinkled over labneh, and in Jerusalem the vendors hand it out in a little bag with the Jerusalem bagel, which itself is topped with nothing but sesame. In Lebanon they say that eating za'atar before school makes children smarter. At the market, buy it by weight and freshly ground, not in a sealed bag off the shelf - the stalls at Machaneh Yehudah and in the souks of the Old City have it in heaps and will let you take a sniff.
The Za'atar I Wanted to Bring Home
Za'atar was one of the things I wanted to bring home from Israel, and in the end I never bought any. I was given some in Jerusalem, at a bakery in the alleys of the Old City where I was buying a Jerusalem bagel: the bakers added it to my bread unprompted, wrapped in newspaper, the way other places slip a candy in with the check. The taste is unlike anything on my spice rack back home. Salt comes first, then a tart wave of sumac, the sesame leaves a nutty richness on the tongue, and the herb a long finish that strikes me as smoky, no matter how much the Arabic sources insist on calling it earthy. I have no price - it was a gift. The bakers called that paper cone by a single word: salt. After the first dipped piece of bagel, I let them have the word - I couldn't have come up with a better one anyway.