Preheat oven 180C (350F). Grease a loaf pan with butter or cooking spray and set aside.
Grab a large mixing bowl. Using a whisk, cream together the butter, brown sugar and white sugar.
Now, add the vanilla extract, egg and unsweetened apple sauce to the bowl and whisk until well combined.
Now add the sourdough starter and whisk it through. The mixture will become thick and marshmallowy.
Lastly, add the flour, baking soda, baking powder and spices into the bowl and use a spatula to gently fold the dry ingredients into the wet ingredients. You don't want to over mix the batter.
Pour the mixture into the prepared loaf pan and smooth the top, ensuring the batter is evenly distributed.
Bake for around an hour at 180C (350F) or until a toothpick comes out clean.
Once the sourdough gingerbread is done, remove from the oven and allow it to cool in the pan for around 10 minutes before inverting onto a wire rack to cool completely.
While the sourdough gingerbread loaf cake is cooling, add all of the frosting ingredients to a bowl and whisk together until light and fluffy (you can use electric beaters if you want to make it easier). Spread onto cooled loaf cake and top with chopped pecans.