Mix the cocoa powder and hot water until smooth.

Let the cocoa mixture cool.

Cream the margarine and caster sugar until light and fluffy.

Beat the eggs and slowly add them to the margarine and sugar mixture.

Add the cooled cocoa mixture to the batter.

Gently fold in the self-raising flour.

Pour the batter into two lined 7-inch cake tins.

Bake at 375F (190C) for 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool completely.

While the cakes cool, cream the butter for the icing.

Melt the good quality chocolate in the microwave.

Mix the melted chocolate into the butter.

Add the icing sugar to the chocolate butter mixture and mix until smooth.

Let the icing cool slightly but do not chill.

Once the cakes are cool, sandwich them together with half of the chocolate icing.

Spread the remaining icing on top of the cake.