Preheat oven to 350 degrees and line the bottom of two 8 inch baking pans with parchment paper and grease the edges. Set aside.
Set the non-dairy milk out to come to room temperature and place the eggs in a bowl of warm water. Set aside.
In a large mixing bowl, whisk together the almond flour, coconut flour, cocoa powder, baking powder, baking soda, and sea salt.
In a medium-sized pot, add the butter and sweetener. Heat over low heat until the butter is melted and the sweetener is mostly dissolved. Then, stir in the non-dairy milk, apple cider vinegar, brewed coffee, and vanilla.
Stir the wet ingredients into the dry. Then add the eggs one at a time, mixing after each one until completely incorporated. Evenly divide the batter between the two cake pans.
Bake 40 to 45 minutes or until a toothpick inserted in the center comes out clean. Since all ovens are different, however, check after 35 minutes to ensure that it's not baking faster and doesn't dry out!
Cool in pan 10 minutes, then invert them onto a cooling rack (removing the parchment paper) to cool completely. Then, wrap tightly in plastic wrap and cool in the fridge for at least one hour up to overnight.
Use room temperature ingredients. Cold ingredients prevent the flours from mixing properly and can interfere with how the cake rises.
Not all brands of coconut flour are the same - some are much more absorbent than others! I only recommend Bob's Red Mill, Besti, or Arrowhead Mills. These are 3 brands that I know will work. If you use a different brand I can't guarantee the results.
While oil can be used, I recommend using grass-fed butter. Grass-fed butter has many health benefits and produces the best texture because oil is a bit heavier. Non-dairy butter can be substituted.
For the sweetener, I recommend an erythritol-based keto sweetener. I prefer a Monk Fruit Erythritol Blend. For paleo, use coconut palm sugar.
Line the pans with parchment paper. If you skip the parchment paper you will have trouble with the cakes sticking to the pans so don't skip it! To line the pans with parchment paper: 1) Place the pans on a large sheet of parchment paper. 2) Trace the bottom of the pans with a pencil. 3) Cut the parchment paper using the lines you traced. 4) Grease the pan, place the parchment paper in the pan, then grease the parchment paper. This will ensure easy removal and the cakes will slide right out.
Don't skip cooling and refrigerating the cake before frosting! Layered cakes are best frosted after they've been refrigerated. However, refrigeration slightly dries out the cake. Because of this, I developed this recipe to bake up overly soft so the texture and crumb will be perfect after refrigeration. Also, the cakes will be much too soft and delicate to frost if they haven't been refrigerated first.
Refrigerate cake after frosting. After the cake is frosted, place it in the fridge for 30 minutes to 1 hour. This allows time for the cake and frosting to re-set, as it were. It will also ensure clean slices without crumbs.