Preheat oven to 350 degrees and line 2 or 3 8-inch baking pans with parchment paper and grease with oil.
Set out butter to bring to room temperature. See the link below for a quick way to bring to room temperature. In a separate bowl, cover the 10 eggs with warm water and set aside so they come to room temperature.
In a medium-sized mixing bowl, whisk together the almond flour, coconut flour, sea salt, baking soda, and baking powder. Break up any clumps with your fingers.
In a large mixing bowl, beat the room temperature butter and sweetener until light and fluffy. It may seem crumbly at first but keep beating until smooth, up to 5 minutes. Scrape down the sides with a rubber spatula if needed.
Beat in the eggs and egg whites one at a time, then the non-dairy milk, vinegar, and vanilla.
Turn mixer to low and beat in the dry ingredients until combined.
Evenly divide the batter between the prepared cake pans. Bake for 28 to 34 minutes, or until a toothpick inserted comes out clean and the top is lightly golden. Since all ovens are different, check after 25 minutes to make sure it's not baking faster to ensure it doesn't dry out - especially if you're making 3-layers!
Allow to slightly cool in the pan, then transfer to a cooling rack (removing the parchment paper) to cool completely. Then tightly cover the cakes in plastic wrap and place in the fridge for at least one hour or up to overnight before frosting for the best texture.
See how easy this recipe is to make on my YouTube channel! Watch the full video here: YouTube Cake Video
For grain-free baking powder combine 1 part baking soda, 2 parts cream of tartar, and 2 parts potato, arrowroot, or tapioca flour.
Nutrition info uses Silk Unsweetened Cashew Milk and does not include frosting. Each serving is 1 cupcake or 1/24th of a cake.
Even if you eat dairy, cow's milk is high in carbs so I recommend unsweetened, non-dairy milk.
Use room temperature ingredients. If the ingredients are cold it can prevent the flours from mixing properly and can interfere with how the cake rises.
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.
Completely cool cake layers before frosting. If you try to assemble or frost the cake, even if it's the slightest bit warm, it will be a disaster! I recommend cooling completely, then placing them in the fridge tightly covered in plastic wrap for several hours to overnight. Otherwise, the cakes are very delicate and hard to frost. They can be refrigerated up to one day before frosting.
Refrigerate cake after frosting. After the cake is frosted, place it in the fridge for 1 hour. This allows time for the cake and frosting to re-set, as it were. It will also ensure clean slices without crumbs.
To check the size of your cake pan, cake pans are measured across the top, not the bottom. Do not measure from the outside edges, as you do not want to include the thickness of the pan. If you are not using an 8-inch cake pan, adjust baking times accordingly.
A word of caution: not all coconut flours are the same! Some brands are much more absorbent than others. Because of this, I only recommend using Bob's Red Mill, Besti, or Arrowhead Mills. These are the brands I know will work. If you need to use another brand, I can't guarantee the results, but look for one that is soft and fluffy, not gritty
For the sweetener, I recommend a granulated erythritol-based sweetener, such as Besti Erythritol or Besti Monk Fruit Erythritol Blend. They're both keto-friendly and have great taste. Granulated Swerve or Lakanto Sweetener (popular erythritol-based sweeteners) will also work. Keto sweeteners take a little longer to incorporate into the butter. When creaming the two together it may take a little longer than usual, up to 5 minutes until it's light, fluffy, and well incorporated.
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Unlike Swerve, which can be used as a 1:1 sugar substitute, Besti Pure Erythritol is only 70% as sweet as sugar so if you decide to use this sweetener you'll need to use an extra ⅓ cup + 2 tablespoon