Melt the butter in a large pot (a wok also works well). Use a blender to semi-puree the onions, carrot and garlic, add to the butter and cook gently until softened. Whisk in the flour and cook for 5 more minutes stirring frequently.
Gradually whisk in the milk, stirring well after each addition. Add the stock, salt and pepper and continue to stir. Simmer for 15 minutes being careful not to let the mixture boil.
Add the potatoes and za'atar. Continue simmering and stir occasionally for 15-20 minutes until the potatoes are soft. Season if necessary with salt and pepper. For a fuller flavour additional stock may be added at this point.
Blend the soup until creamy. Simmer for a further 5 minutes and allow the soup to rest for a few minutes before serving. Skip the blending or blend only half of the soup if preferred.
This soup can be served warm or hot. Serve with toasted, buttered pitta bread or a traditional Moroccan bread.
Zaatar is one of the most ancient and traditional spice blends in the world. People have been writing down ways to cook with zaatar for literally thousands of years. From simple Zaatar-marinated olives or hummus flavored with Zaatar to complex stuffed flatbreads and the famous Lebanese sandwiches.
Zaatar can refer to both the thyme-based spice blend and thyme itself, and ancient references to Zaatar do not make great effort to clarify which one they are referring to. There are some good sources on the history of zaatar. Twelfth century Jewish philosopher Maimonides described the Zaatar blend as an excellent brain food. Just a few years ago conflict erupted in the Holy Land when Israel temporarily banned the transport of Zaatar only to quickly reverse the ban after some protest. Basically, when we start talking Zaatar, we’re talking about a blend with deep historical and emotional roots.
Zaatar is generally regarded as a finishing spice. In other words, it’s best to put a healthy sprinkle on top of something you’ve already prepared like hummus or even a nice grilled meat. One of the more popular ways to make use of its savoury bite is to make a flatbread, which is a great support bread for a Lebanese sandwich. If you want to go in a heartier direction, try a nice potato pancake with Zaatar. While you can't just put Zaatar on anything, the savoury combination can kick up a lot of your favourite foods. That is, after all, what’s it’s been doing for thousands of years.