Preheat your oven to 350°F and line 2 9-inch cake pans with parchment paper, rubbing down the sides of the pan generously with coconut oil.
In a large bowl, stir together the almond flour, coconut sugar, tapioca starch, cacao nibs, baking soda, and salt. Add the banana, but don’t mix it in.
Make 3 large wells in the flour. Pour the coconut oil in the first well, the vinegar in the second, and the vanilla extract in the last well. Don't mix yet.
Add the water and mix well with a fork, making sure the banana is evenly incorporated.
Divide the batter between the 2 pans, spreading out evenly. Bake until deeply golden brown and a toothpick inserted in the center comes out clean, about 26-28 minutes.
Let the cakes cool in the pan for 30 minutes before transferring to a wire rack to cool completely.
Make the ganache by whisking together the coconut milk, almond butter, and honey or agave in a small pot over medium heat.
Whisk until the almond butter is smooth and melted and the mixture begins to steam and is just about to boil (you’ll start to see a few small bubbles).
Remove the pot from the heat, add the chocolate, and let it stand, without whisking, for 30 seconds. Then, whisk until the chocolate melts and the mixture is smooth.
Transfer the ganache to a bowl and place into the refrigerator to thicken and cool slightly for 1 1/2 hours.
Once cooled, gently place one of the cakes bottom-side up onto a cake stand and use an offset spatula to spread about 1/2 cup of ganache on it. Place the other cake bottom-side up on top. Note: These cakes are very delicate, so if you have trouble flipping them without breaking them, it’s alright to place them bottom-side down.
Spread a very thin coat of ganache on the top and sides of the cake, just to seal in the crumbs. Refrigerate until the ganache is set, about 30 minutes. Keep the remaining ganache at room temperature.
Once the crumb coat is set, spread the remaining ganache on the top and sides of the cake. Garnish with additional cacao nibs, if desired.
Place the cake back into the refrigerator for 30 minutes to set.
