Oil the cake molds and preheat the oven to 325℉. Attach a round tip to the piping bag or use a plastic Ziploc bag with a cut corner.
In a small mixing bowl, combine the Keto Chow, cocoa powder, and baking powder.
Beat the egg whites in the work bowl of an electric mixer with the whip attachment until they begin to look frothy. With the mixer at medium speed, add the cream of tartar and sprinkle 1/4 cup of the powdered erythritol over the egg whites. Beat until the egg whites look glossy and hold stiff peaks.
Transfer the beaten egg whites to another bowl and place the egg yolks in the work bowl. (No need to wash the bowl yet.) Beat the egg yolks with the remaining 1/4 cup powdered erythritol until they have doubled in volume, which should take about five minutes. They should look satiny and be light yellow in color.
Fold the avocado oil and vanilla extract into the egg yolks with a rubber spatula.
Fold the egg whites into the egg mixture in two portions.
Sprinkle the Keto Chow mixture over the eggs and fold in gently. The volume will decrease slightly.
Fill the piping bag with the batter and pipe into the prepared cake molds.
Bake the cakes for 15-20 minutes, or until they have risen, the surface looks dull, they spring back when touched, and a cake tester comes out clean.
Set the molds on a cooling rack. Turn the cakes out of the molds when they have cooled for about five minutes, then let cool completely.
To make the filling, beat together the peanut butter and softened butter until light and fluffy. Add the Keto Chow, erythritol, heavy cream, and vanilla extract and beat until combined and light.
Put the filling in a piping bag with a large star tip or ruffle tip, or in a Ziploc bag with a cut corner to create a piping bag.
Carefully slice the cooled cakes in half lengthwise.
Pipe filling on one half and place the other half on top, then place in the refrigerator to set. Reserve about 1/4 cup of the filling to decorate the cakes.
To make the glaze, sift the powdered erythritol and cocoa powder into a mixing bowl.
Add the vanilla extract and stir in the warm water a tsp. at a time until it reaches a thick, pourable consistency.
Spoon or pour the glaze over the top of each cake, smoothing it to the edges.
Allow the glaze to set slightly, then decorate the tops with the remaining peanut butter filling. They can also be decorated with crushed peanuts, shaved chocolate, or whipped cream.
Store in an airtight container in the refrigerator for up to three days or store frozen for up to three months.