Ka'ak b'Za'atar (كعك بالزعتر) is the sesame street bread filled with za'atar, the herb, sumac, and sesame blend slackened with oil, and it is the canonical treatment of the loaf, the one most carts reach for by default. The angle is two sesame-forward, complementary things meeting: the toasted sesame crust and faint sweetness of the ka'ak on one side, and the za'atar mix, itself heavy with sesame and sharpened by sumac, on the other. There is no protein and no cheese to manage, so the whole sandwich hinges on the za'atar being good and on the oil binding it to a warm crumb rather than leaving it dry and dusty.
The build is minimal and the craft is in the paste and the warmth. The ka'ak is heated so the sesame crust re-crisps and the inside softens, then split along its wider belly. Za'atar is loosened with a generous pour of olive oil into a spreadable paste and painted into the warm pocket so it soaks into the crumb instead of sitting as loose powder; the loaf is often given a brief reheat so the oil and herb meld into the bread. The judgment calls are the za'atar quality, the oil ratio, and the heat. A stale or over-dried blend tastes flat and gritty; a fresh one is green, tart with sumac, and nutty. Too little oil and the filling is dusty and parches the bread; too much and it goes greasy and slides. A cold loaf leaves the paste stiff and the flavors closed; a warm one opens them. A good ka'ak b'za'atar is warm and fragrant, the herb tart and nutty, the oil carrying it into a crisp-shelled, faintly sweet crumb; a poor one is dry, dusty, or oily in a stale loaf.
It varies by what is added to round out a deliberately spare base. White cheese is the most common partner, the ka'ak za'atar-and-cheese being a standard order; sliced tomato, cucumber, mint, olives, or a smear of labneh also turn up to add moisture and contrast. The za'atar itself differs by blend, some heavier on thyme, some on sumac, some on sesame. Within the ka'ak family it is the foundational filling, the reference point the cheese, egg, labneh, and sweet versions are measured against. It is essentially the za'atar manoushe idea in a different bread: the same herb paste that coats a flatbread, here painted inside the warm sesame loaf and judged on the paste and the bind.