To make the cake, whisk together the flour, 1 1/4 cup cocoa, buttermilk powder, baking powder, salt, and baking soda in a medium mixing basin. Remove from the equation. 30 seconds on medium to high speed, whip butter in a large mixing bowl with an electric mixer. Gradually add brown sugar, beating until light and fluffy, about 5 minutes. Blend in the vanilla extract and coffee crystals. One at a time, add the eggs, beating for 1 minute after each addition and scraping the sides of the basin often. On low speed, beat in one-third of the cocoa mixture and 1/2 cup of water until fully blended. Repeat with the remaining 1/2 cup of water and one-third of the cocoa mixture, beating on low speed just until well blended.