Preheat oven to 350 degrees F (180 degrees C) and place oven racks in the upper and lower third of the oven. Lightly butter and flour line the cake tray or baking pans with parchment or wax paper.

In a heatproof bowl, placed over a saucepan of simmering water, melt the chocolate.

Remove from heat and let cool to room temperature.

In a separate bowl, sift the flour, cocoa powder, baking powder, baking soda, and salt.

In a small bowl, combine the coffee (or water) and buttermilk.

In the bowl of your electric mixer, or with a hand mixer, beat the butter until smooth and creamy. Add the sugar and continue beating until the mixture is fluffy.

Add the eggs, one at a time, mixing well after each addition. Add the vanilla extract and beat to combine. Then add the melted chocolate and beat until incorporated.

Add the coffee/buttermilk mixture and flour mixtures in three additions, beginning and ending with the flour mixture. Beat only until the ingredients are mixed together.

Pour the batter in to the prepared baking tray. Bake for about 30 - 35 minutes or until a toothpick inserted in the center comes out clean and the tops spring back when lightly pressed.

Let it to cool completely before cutting the cake.