Add the white rice flour, tapioca flour, corn starch, brown rice flour, xanthan gum, baking powder, salt, and chopped spring onions in a bowl. Using a whisk, combine the ingredients.
In a separate bowl, add the eggs, olive oil, and yogurt. Using a whisk or handheld mixer, combine the ingredients. Then add the shredded mozzarella cheese, black olives, Zaatar, sumac, apple cider vinegar, fresh thyme leaves and gently mix until combined. Then add the flour mixture and mix gently using a spatula until combined. The batter will be thick.
Grease a 25 cm (10 inches) cake tin with butter, then add and spread the savory cake batter to fill the cake pan.
Now bake the savory cake for 20-25 minutes, or until a toothpick inserted at the center comes out clean.
Notes
Storage & Freezing: The savory cake can be stored in an air-tight container in the fridge for up to five days. To freeze the savory cake, wrap it in plastic wrap followed by aluminum foil. The cake can be frozen for up to three months.