Start by preheating your oven to 180C/160C fan/gas 4 and grease and line three 8” cake tins.
In the bowl of a stand mixer (or a large mixing bowl), cream together the butter and sugar until light, fluffy and pale in colour.
Crack the eggs into a separate bowl and beat until smooth.
Running the mixer on a low speed, begin to add the beaten eggs to the butter/sugar mixture a little at a time. If the mixture starts to curdle, add a tablespoon of flour.
Sieve the flour, cocoa powder and instant coffee powder into the bowl and mix until just combined. Be careful not to over-beat the mixture.
Divide the mixture equally between the three tins and level off with your spatula, before baking in the preheated oven for around 30 minutes (until the cakes are soft and springy to the touch and a skewer comes out clean).
Once your cakes are baked, remove them from the oven and leave to cool in the tins for around 5-10 minutes, before inverting onto a wire rack to cool down completely.
To make the buttercream, begin by breaking up your chocolate into cubes and placing in a microwave-safe bowl.
Heat the chocolate in a microwave for 30 seconds, before stirring. Continue to heat and stir in 30 second intervals until the chocolate is completely melted.
Set the chocolate aside to cool for five minutes while you cream your butter in the bowl of a stand mixer until pale and smooth. This may take a while, but the longer you leave it, the better.
Add in half of the icing sugar and mix on a low speed until it is fully incorporated. Add the second half of the icing sugar and again mix until fully incorporated. This shouldn’t take more than 1 minute.
Finally, add the cocoa powder, the melted chocolate and the milk, and mix again until smooth.
Cover the bowl of buttercream with clingfilm and set aside until ready to use.
When your cakes have fully cooled and you are ready to assemble your cake, begin by giving your buttercream a final pulse in the stand mixer.
Place one of the cake layers right-side up onto your serving plate and pipe ‘kisses’ around the edge of the cake. Fill the centre of the cake with more of your buttercream, using an offset spatula to ensure it is evenly distributed.
Add the next layer of cake and repeat the above step, piping kisses and filling the centre.
Next, add the top layer of cake and cover it entirely with piped ‘kisses’.
Finally, scatter over a handful of sprinkles and set aside until ready to serve.