Preheat your oven to 160/140C Fan, and line a 9x13" tin with parchment paper.
In a heatproof bowl, microwave the dark chocolate and butter until melted – mine takes two minutes!
Pour the coffee granules into 125ml boiling water and mix – add the coffee to the chocolate/butter mix and stir well until smooth!
In a separate large bowl add the plain flour, cocoa powder, baking powder, bicarbonate of soda, golden caster sugar, and light brown sugar and mix well so the ingredients are all mixed with each other!
Mix the eggs with the buttermilk
Add the chocolate mix & the egg mix to the dry ingredients and stir together. (Try not to over mix it – you don't need to use an electric mixer, just use a bowl and a spatula.)
Pour the mixture into the tin and bake in the oven for 50-60 minutes (can take a little longer in some ovens). Once baked, leave to cool in the tin and remove afterwards, or leave for 10-15 minutes and cool on a wire rack for a softer cake.
For the Frosting
With an electric mixer with the paddle attachment, beat the butter until its very smooth and supple (couple of minutes)
Gradually add the icing sugar with the evaporated milk, making sure to alternate between the two, until all is incorporated.
Add the vanilla extract – beat for a couple of minutes so it's extra smooth & creamy.
The more evaporated milk you add the more runny it’ll be, and I have found about 75ml-100ml is perfect for this one!
Slather the buttercream onto the cake, and decorate with your favourite Easter chocolates! ENJOY!
Notes
This cake will last for 3+ days at room temperature.
I 100% would stick with using the coffee in the cake, you can't taste it, but it helps the chocolate flavour so is important.
The cake can take longer to bake if its over mixed - be as gentle as possible with it.
If you can't access buttermilk, you can make your own by using 100ml of FULL FAT milk, mixed with 2tbsp of lemon juice! It will look curdled but this is fine.
Use whatever type of Easter chocolates you fancy on top of the cake - as many or as little as you fancy!