Za'atar is a type of wild thyme often mixed with sumac (a brick-red, sour spice), salt and sesame seeds. You can find it in Middle Eastern markets.
In a large bowl, beat yogurt until light and smooth. Scrape into a shallow, wide serving bowl and smooth with back of a spoon to create a wide indentation. In a small bowl or liquid measuring cup, whisk oil and lemon juice until emulsified; season well with salt and pepper. Pour vinaigrette over yogurt so it floods indentation. Sprinkle with pine nuts and za'atar. Taste, adding a bit more salt, if desired. Serve with pita.
Recipes adapted with permission from the publisher, Houghton Mifflin Harcourt, from "Yogurt Culture" by Cheryl Sternman Rule. Copyright © 2015