Line three 20cm (8in) round baking tins with parchment and preheat the oven to 190*C/Gas Mark 5.

Sieve the flour into a small bowl and set aside. Put the butter and caster sugar into a large bowl and beat together until light and fluffy. Add two eggs to the bowl and beat well.

Sieve the cocoa into the bowl and stir to combine. Add the remaining eggs, beating them in one at a time.

Beat in half the prepared flour followed by the milk and vanilla. Stir in the remaining flour, then divide the mixture between the prepared cake tins and smooth the top. Bake for 30-35 minutes.

Put the butter into a bowl and beat it until it is light and fluffy. Sieve the icing sugar into the bowl and beat to combine.

Divide the mixture between the top of two cold cakes and spread it out evenly. Place one cake on top of the other. Place the third sponge on top.

Put the cream into a saucepan over medium heat. When it is almost boiling, remove the pan from the heat and stir in the chocolate.

Allow the topping to cool stirring until it thickens slightly, then spread over the top and sides of the cake.

Scatter marshmallows over the cake, then sieve a little cocoa over the top to finish.