Step 1 - Butter and line 2x20cm/8inch and 10cm/4inch high round tins. Preheat oven to 160C/320F. Whisk the sugar, flour, cocoa, bicarb and baking powder in a large bowl. In a large jug measure the buttermilk, oil and vanilla. Beat in the eggs and then the water. Mix gently into the flour mixture in 3-4 lots along with the chopped chocolate. Divide among the two tins and bake for 30 minutes.

Step 2 - Fit a beater attachment to your mixer and beat the butter, sugar and cocoa together on low speed for 1 minute and then increase it to a speed of 3 out of 10 for 3 minutes. Add the water and vanilla in at low speed and beat on the same speed (3 out of 10) for another 5 minutes or until the sugar no longer feels gritty between your fingers.

Step 3 - Trim the tops off the cakes (I made cake pops with the extras) and then slice each cake in half horizontally using a cake leveller (I am pretty hopeless at achieving a straight slice with a knife). If you have time, please cover and freeze the cake layers so that they are easier to ice. Spread the buttercream between each layer of cake and then coat with more buttercream (the cake isn't overly crumby so I didn't really need a crumb coat).

Step 4 - Fit a piping bag with a 1A tip and fill with some of the buttercream and pipe dollops around the edge of the cake. Then top with black cherries, blackberries and sprinkles.