Classic chocolate cake

Method

1. Grease and line the base of two 22cm (8in) round cake tins and preheat the oven to 180°C/350°F/gas 4.
2. Put the butter, caster and muscovado sugars into a bowl and beat together with an electric whisk until light and fluffy. Add the eggs one at a time, beating well between each addition.
3. Sieve the flour, cocoa, baking powder and bicarbonate soda into the mixture, then pour in the sour cream or buttermilk.
4. Stir everything together to create a smooth mixture and spoon into the prepared cake tins.
5. Bake for 20-25 mins until just firm and shrinking away from the sides of the tin. Push a cocktail stick into the centre, if this comes out clean, the cake is ready.
6. Cool in tins for 5 mins then turn onto wire rack to completely cool.
7. Sieve the icing sugar and cocoa into a bowl, then pour in the butter and 2tbsp of boiling water. Stir together to make a smooth spreading consistency. If it's too stiff, very carefully add a little more boiling water, drop-by-drop.
8. Spread half of the icing onto the base of one chocolate sponge, sandwich together with the other chocolate sponge. Spread the remaining icing over the top of the chocolate cake, using a palette knife dipped in hot water. Sprinkle over grated chocolate to decorate.