* Two 20 cm (8-inch), shallow cake tins, greased and base-lined.
For the cake, cream together the butter and sugar until the mixture is light in colour anti texture. Gradually beat in the eggs, and then the soured cream (the mixture looks curdled at this stage). Sieve together the dry ingredients and fold them into the mixture. Divide the mixture equally between the tins. Bake at Gas Mark 5/190ºC:/375ºF for 30 – 35 minutes, until cooked. Turn out on to a wire tray to cool.
Make the filling by mixing the cocoa with 40 ml (2 Tbs) of boiling water to a smooth paste, allow to cool. Beat together the butter, sieved icing sugar and essence, until light and fluffy. Beat in the cocoa. Slice the cake in half and then sandwich the halves together with the filling.
For the frosting, melt the chocolate carefully. 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 in slices, with whipped cream or ice-cream. If possible warm each slice in a microwave or oven, if you have made the cake in advance; it can also be served cold but is definitely more interesting hot, with the contrast of ice cream.