Preheat oven to 180°C / 350°F (160°C fan-forced).

Baking pan - Butter a 40 x 28.5 x 2.5cm cm tray (15.8 x 11.3 x 1" - US standard jelly roll pan) then line with baking paper (parchment paper).

Whisk dry - Sift the flour, cocoa, baking powder and baking soda into a bowl. Add the sugar and salt, then whisk to combine.

Mix in wet - Add the egg, milk, oil and vanilla. Whisk to combine. Dissolve the coffee in the hot water, then add into the batter. Whisk to combine. The batter will be VERY thin!

Bake - Pour into the pan and bake for 13 minutes.

Cool for 10 minutes then use the paper overhang to lift the cake onto a rack and cool for 30 minutes (leave it on the paper). Then refrigerate uncovered for at least 1 hour before cutting rounds (cake is too soft when freshly baked).

Cutting rounds - Cover the sticky surface with paper. Then flip upside down onto a cutting board (ie sticky side down). (Note 4) Peel the paper off the base. Then press out 21 x 6cm / 2.4" rounds (or other size or shape as you desire).

Pipe frosting - Place a piece of cake on a small piece of paper, using a dab of frosting to stop it from sliding. Pipe coils of frosting on the layers, using 3 rounds for each cake. Pipe frosting around the sides and on the top. (A cake turntable is handy if you've got one but not essential.)

Smooth frosting - Smooth the frosting using a small offset spatula or knife, taking care to only touch the surface. Avoid touching the cake because it will dislodge crumbs that will end up in your frosting!

Decorate with piles of chocolate shards. I also used raspberries and rosemary for the photos in the post!

Beat butter for 3 minutes on high until soft and fluffy. Add icing sugar in 3 lots. Beat it in, starting on low speed then increasing the speed (to avoid a snow storm). Once incorporated, add more icing sugar and repeat.

Beat 3 minutes - Once the icing sugar has all been added, added the cocoa powder, milk and vanilla. Beat again, starting on low speed then increasing the speed gradually. Once the cocoa is incorporated, beat on high for 3 minutes to make it really nice and fluffy.

Piping bags - Transfer to a piping bag for frosting. (This is the fastest and easiest way, trust me on this. Even a ziplock bag will work here).