Melt butter, dark chocolate, sugar, and cocoa in a large pan over low heat.

Stir gently until well combined.

Add hot water and stir until smooth. Cool the mixture.

Sift plain flour and self-raising flour together in a separate bowl.

Add the sifted flours to the cooled chocolate mixture.

Stir in the beaten eggs until just combined.

Pour the batter into a lined cake tin.

Bake in a preheated oven at 170 degrees Celsius for 1 hour.

Let the cake stand for 5-10 minutes before turning it out from the cake tin.

Melt the remaining dark chocolate over gentle heat for the icing.

Stir in cream and mix well until smooth.

Ice the cooled mud cake with the chocolate icing.