- Preheat oven to 350-degree F.
- Mix cocoa, baking soda, salt and flour in a big bowl.
- In a separate bowl, with an electric mixer, cream the butter and sugar.
- Add flax egg and vanilla.
- Add dry ingredients.
- Form into 2-inch balls and flatten slightly.
- Bake for 9-11 mins.
- Whisk together all frosting ingredients with an electric mixer.
- Put into a piping bag.
- Once the cookies have cooled, pipe frosting onto one cookie and place another cookie on top to form a sandwich.