Pre-heat the oven to 180°C; line a 9×5-inch loaf pan with baking parchment, greasing well.
Sift the flour, baking soda and cocoa powder in a mixing bowl, whisk well to combine and set aside.
Cream the butter and sugar in a separate bowl until light and fluffy (preferably using an electric hand-held mixer); next, beat in the eggs and vanilla extract.
Fold in the melted chocolate (make sure it’s slightly cool) until combined well. But don’t over-mix!
Fold in the dry ingredients (the mixture of flour, cocoa powder and baking soda) into the liquid mixture in batches, alternating with the hot coffee & boiling water.
Your final batter will be smooth and relatively runny. Pour it into the pan and bake for 30 minutes, after which time turn the oven down to 160°C and bake for another 12 minutes or so until a toothpick/ knife plunged in the centre comes out mostly clean but with some moist crumbs attached.
As tempting as it is to tuck in straight away, leave the loaf pan to completely cool down on a wire rack before slicing the cake.