To make the cake:

• Grease and line a 20cm cake tin. Preheat your oven to 180C.
• Break the chocolate into pieces and add it to a heatproof bowl along with the cocoa and espresso powder or coffee, if you’re using it. Pour over the boiling water and stir to combine. Set aside to melt, and if there are still some chocolate chunks left, pop it over a small saucepan half filled with water over a medium heat until smooth.
• Combine the remaining dry ingredients in a medium mixing bowl and whisk well. Add the eggs, olive oil and milk and whisk until a batter forms.
• Use a spatula to scrape the chocolate mixture into the batter and whisk again until everything is combined. The batter should be a chocolate colour and slightly on the runny side.
• Decant the batter into the lined cake tin and bake for 35-40 minutes or until a skewer comes out clean. Remove the cake from the oven and allow to sit for 10-15 minutes. Run a knife around the edge of the cake to gently remove it, then place on a baking rack to cool.

To make the chocolate buttercream icing:

• Beat the butter in a stand mixer or using hand beaters until light and fluffy. The timing depends heavily on how soft your butter is and whether your kitchen is hot or cold. Once fluffy, add the sifted icing sugar and continue beating until pale and fluffy. Add the cocoa and beat until combined. Add the milk or cream, a tablespoon at a time, until your desired consistency is achieved. Add a pinch of salt to taste.
• When your cake has cooled completely, ice it with as much buttercream as you fancy. Best served the day of icing, but leftovers keep well in the fridge in an airtight container for a number of days.

OR

To make the chocolate ganache icing:

• Thoroughly chop the chocolate into fine pieces and transfer into a medium heatproof bowl. Fine chocolate shards help the chocolate to melt quickly and evenly.
• Heat the cream to a simmer in a small pot over a medium heat. Steam should be rising up and small bubbles starting to appear, but it should not be bubbling wildly. If the cream is too hot it risks splitting the ganache.
• Pour the hot cream over the chocolate shards and allow to sit untouched for 5 minutes. Be careful not to let any liquid into the bowl or the mixture might split. After that time, whisk to combine. If the chocolate isn’t completely melted, place it over a small bowl of boiling water and whisk intermittently until all chunks are gone.
• Remove the bowl from the hot water bowl and set aside to cool for 15-20 minutes, or until the ganache has reached a spreadable, thick consistency. Place the ganache onto the cake and use an offset spatula or the back of a spoon to spread it evenly over the cake and create a lovely swirled top. Finish with some sea salt flakes, sprinkles, if you like, and serve.