Pre-heat oven: 180°C / 160°C (fan) / Gas Mark 4 / 350°F
In a heatproof bowl, melt the chocolate slowly in the microwave (15-30 secs at a time) and stir until smooth.
Add the oil into the melted chocolate and mix until combined.
In a separate bowl, beat the eggs, sugar, milk and vanilla together, then pour the chocolate-oil mixture into this, mixing until fully combined.
In a different bowl, sieve the cocoa powder, flour, baking soda and baking powder, whisking together until fully mixed.
Gradually pour the wet ingredients into the dry, stirring together as you pour until just combined. There may be a few small lumps left, but that’s ok.
Slowly add the hot coffee to the mixture, stirring as you pour until only just combined. The cake mix will be very liquid.
Divide the cake batter evenly between three lined cake tins and bake for 30-35mins, until the sponges no longer wobble, are firm to touch and a skewer comes out clean.
Allow the sponges to cool on a wire rack while you make the buttercream.