Put some water on to boil in the kettle and preheat the oven to 180°C/ 350°F/ GM 4.
Grease and line 4 x 6-inch tins or 3 x 8-inch tins* see notes.
Melt the chocolate either in the microwave or using a bain-Marie.
In a large bowl, cream the butter and sugar together using electric beaters until they are lighter and fluffy in texture. This will take approximately 3 minutes.
Add the eggs, 1 at a time, beating well between each addition.
Mix the cocoa powder and 3 tablespoons of the water from the recently boiled kettle together to form a smooth paste. Add this to the cake batter and beat until well combined.
Pour in the melted chocolate and mix again.
Sieve the flour, baking powder and bicarbonate of soda into a bowl.
Pour half of the buttermilk into the cake batter mix and mix in in.
Add half of the flour mixture and mix it in briefly.
Repeat with the remaining buttermilk and flour
Add 275ml recently boiled water and stir until it is just combines.
Pour equal amounts of batter into the cake tins and put them into the over the bake. This will take around 25-30 minutes for the 6-inch cakes and 30-35 minutes for the 8-inch cakes.
Check that the cakes are cooked by inserting a metal skewer into the centre - it should come out clean. Once cooked, take the cakes out of the oven and let them stand for 2 minutes, before removing them from the tins and allowing them to cool on a wire rack.