Directions

1. Preheat oven to 350F (175C). Line baking sheets with parchment paper.
2. In a bowl, whisk together flour, cocoa powder, baking soda, and salt.
3. Cream butter and brown sugar until fluffy.
4. Beat in egg and vanilla extract to the butter mixture.
5. Alternately add dry ingredients and buttermilk, starting and ending with dry ingredients.
6. Drop batter by tablespoons onto baking sheet in rounds.
7. Bake 8-10 minutes until tops spring back lightly.
8. For filling, beat powdered sugar, softened butter, and vanilla until smooth and fluffy.
9. When cookies cool, sandwich filling between two cookies.
10. Serve chilled or at room temperature.