Preheat your oven to 180 degrees C and place the oven rack in the center of the oven. Butter or spray an 20 cm square baking pan with a non stick cooking spray. Line the bottom of the pan with parchment paper
In a large bowl whisk or stir together the flour, sugar, cocoa powder, baking powder, baking soda, and salt
Add the melted butter, water, vinegar, vanilla extract, and coffee extract (if using). Mix all the ingredients together until well blended.
Pour the batter into your pan and bake in preheated oven for about 28 - 30 minutes, or until the cake springs back when lightly pressed and a toothpick inserted in the center of the cake comes out clean. Remove from oven and place on a wire rack to cool for about 10 - 15 minutes before removing the cake from the pan
Ganache: Place the chocolate in a medium sized stainless steel, or heatproof bowl. Set aside. Heat the cream and butter in a medium sized saucepan over medium heat (can also be heated in the microwave). Bring just to a boil. Immediately pour the cream over the chocolate and allow to stand for a few minutes. Stir until smooth, then let stand at room temperature until the Ganache has completely cooled and set to spreading consistency. Spread the Ganache on the top and sides of the cake.