Found this in a Cadbury's book for American Chocolate Fudge Cake (also known as "Death by Chocolate")
For the cake
4oz butter
8oz dark soft brown sugar
2 eggs
1/4 pint soured cream
6oz plain flour
1 tsp baking powder
1/2tsp bicarb of soda
2oz Cadbury's Bournville cocoa
Filling
2tblsp Bournville cocoa
4oz butter
5oz icing sugar
vanilla essence
For the frosting
200g bar of Cadbury's Bournville chocolate
2tblsp Cadbury's Bournville cocoa
1/4 pt double cream
2x20cm (8 inch) shallow cake tins, greased and base-lined.
For the cake, cream butter and sugar until mixture light in colour. Gradually beat in eggs and then soured cream (mixture looks curdled at this stage). Sieve together dry ingredients and fold in to mixture. Divide equally between tins. Bake for 30-35mins at Gas 5, 190C,375F. Turn out and allow to cool.
Make the filling by mixing the cocoa with 2 tblsp boiling water to make a smooth paste, allow to cool. Beat together butter, sieved icing sugar and vanilla essence, until light and fluffy. Beat in the cocoa. Sandwich the halves together
For the frosting, melt the chocolate. Make the cocoa into a paste with water as before and mix with the chocolate. Slowly whisk the cream into the chocolate until smooth and thickened. Spread the frosting evenly over the cake with a palette knife.
Serve with ice cream or cream. If possible warm each slice in the microwave or oven.
But I'm sure MarsLady can come up with something equally chocolatey