Preheat oven to 170C (338F). Grease a cake pan with butter and set aside. I've used a square pan 10" x 10" or 22.5cm x 22.5cm.
In a large mixing bowl add all of the dry ingredients - all purpose flour, brown sugar, baking powder, baking soda, salt, cinnamon, nutmeg and ginger. Mix together until well combined.
In the centre of the dry ingredients, create a well and add all of the wet ingredients to it - sourdough starter, egg, olive oil, Greek yogurt, applesauce and vanilla.
Stir the wet ingredients together in the well and then combine with the dry ingredients to form a batter.
Pour the cake batter into the greased cake pan.
Bake for 40 minutes at 170C (338F). You can check the cake is done by inserting a skewer in the centre. If it comes out clean, you can remove it from the oven. It's ok if it needs a few more minutes to cook through.
Allow the cake to cool in the pan.
Frost with vanilla yogurt glaze or dust with powdered sugar to serve.