Low-Carb Chocolate Whoopie Pie (0.8 g net carbs)

I originally decided to make these because I had leftover donut batter, and I'm thrilled with the outcome! The recipe is almost identical with the exception of the filling. 

Ingredients:
1 cup erythritol
1/2 cup flaxseed meal
2 tbsp almond flour
4 tbsp coconut flour
6 tbsp unsweetened cocoa powder
1 tsp baking powder
1 tsp baking soda
1/2 tsp salt
1 egg
1 cup oil
1/2 cup almond milk
1 tsp vanilla extract
1/2 cup boiling water
2 oz. unsalted butter, softened
2 oz. cream cheese, softened
1 cup powdered erythritol
1/2 tsp vanilla extract

Directions:
Preheat oven to 350 F. Sift together dry ingredients. Beat together the egg, oil, and almond milk and add the mixture to the dry ingredients. Beat for 2 minutes, then add the boiling water. Once combined, add the vanilla extract. Pour into oiled whoopie pie pan or mini-muffin tin. Bake for 8-10 minutes. Once cooled, refrigerate for 30 mn - 1 hour. In the meantime, whip together the butter, cream cheese, powdered erythritol, and vanilla extract. Sandwich between the cookie pieces. Make in advance and keep in the fridge or freezer!

Recipe make approximately 24 regular sized whoopie pies (or 48 made from a mini-muffin tin) with the following nutritional information:
126 calories
13.2 g fat
2.5 g carbs
1.7 g fiber
0.8 g net carbs
​1.1 g protein