In a large bowl, whisk together the orange juice and zest, egg yolks (reserve the egg whites), coconut oil, honey and vanilla.
In a separate bowl, mix the almond flour, coconut flour, baking soda and salt.
Mix the wet and dry ingredients gently with a spatula being careful to not over mix the batter.
Using a stand or hand mixer, whisk the reserved egg whites and lemon juice until stiff peaks form. Mix half of the mixture into the batter gently, then mix the other half.
Divide the batter into 2 bowls and mix the cacao powder with one of the half's.
Alternately, layer your prepared pan with the chocolate and vanilla batter, starting with the chocolate batter. Add a large spoon of the chocolate batter in the center of the pan, followed by the vanilla batter on top and so on.
Tap the pan gently on the counter and bake for 40 minutes, or until a toothpick inserted into the center comes out clean. Set pan on a cooling rack and allow it to cool for 10 minutes before removing the cake from the pan. Dust the top with maple sugar if desired.
Store cake in an airtight container in the fridge. The cake gets better with time in my opinion and will last at least 2 months in the fridge. You can freeze it too.*If you bake this cake with coconut flour omit the 1 tablespoon (8g) of coconut flour listed in the ingredients and add just a total of 55g (1/2 cup). It may also take less time to bake (about 35 minutes) and the cake will be a little smaller.