Preheat your oven to 350℉. Then grease a 9 x 13 cake pan and line with parchment paper. Set aside.
Add the almond flour, tapioca flour, baking soda, baking powder, salt, and cacao powder to a medium mixing bowl. Whisk to combine and set aside.
214 g almond flour, 56 g tapioca flour, 1 tsp baking soda, 1/2 tsp baking powder, 3 g salt, 40 g raw cacao powder
To a separate large mixing bowl, add the starter, eggs, yogurt, maple sugar, avocado oil, and vanilla extract. Mix well with a hand mixer.
100 g grain-free sourdough starter, 4 large eggs, 69 g plain yogurt, 226 g maple sugar, 119 g avocado oil, 2 tsp vanilla extract
Add the dry ingredients to the bowl with the wet ingredients and mix on low speed until almost fully incorporated. Finish combining with a rubber spatula until no dry flour remains.
Pour the cake batter into the prepared cake pan and bake for 35 minutes or until a toothpick inserted in the middle of the cake comes out clean.