Step 1

Preheat an oven to 375 degrees F. Line a 9-inch round cake pan with a large sheet of parchment, pressing it into the edges of the pan and leaving an overhang on 2 sides (the extra parchment will help you unmold the loaf later).

Step 2

Whisk the whole wheat flour, bread flour, sugar, za'atar, lemon zest, salt, baking soda and baking powder together in a large bowl. Whisk the buttermilk, melted butter and egg together in a separate bowl or liquid measuring cup until combined. Make a well in the center of the dry ingredients and pour the buttermilk mixture into the center. Use a wooden spoon or rubber spatula to stir the mixture until it starts to come together in a shaggy mass.

Step 3

Lightly dust a work surface with flour. Turn the dough mixture out onto the floured surface and knead a few times to bring it together. Shape it into a domed disk that’s about 7-inches in diameter. Place the dough into the prepared pan and cut a cross about 1/2 inch deep into the center of the dough using a sharp knife. Brush the top and sides with more buttermilk, then sprinkle with a few good pinches of za’atar and the sesame seeds.

Step 4

Bake until the top is puffed and lightly browned and a toothpick inserted in the center comes out clean, about 1 hour. Remove from the oven and use the parchment overhang to lift the bread from the pan. Place on a wire rack to cool completely.