In a large bowl, sift together cassava flour, cacao powder, coconut sugar, baking powder, baking soda, optional espresso powder, and sea salt.
Add in unsweetened applesauce, dairy free milk, apple cider vinegar, and vanilla extract. Mix either with a spoon or hand mixer until thoroughly combined.
Fold in zucchini and mix again until the zucchini is evenly spread throughout.
Divide batter evenly amongst the 3 pans and place into the oven to bake for 30-35 minutes.
Remove the cakes from the oven and let cool for 15 minutes before leveling out.
Let cool completely before frosting.
When ready to prepare the vegan buttercream, use a hand mixer to beat the softened vegan butter until it’s whipped and it begins to increase in volume.
Sift in cacao powder and continue to beat.
Slowly add in coconut sugar in 1/2 cup increments until it becomes a nice and thick buttercream. To help with the consistency, add in a tbsp of dairy free milk at a time until it reaches a soft, moveable yet firm consistency.
Frost each layer and serve! Store in the refrigerator to keep the buttercream from melting, and let it sit out on the counter for 15 minutes to soften.