Chocolate and Mango Gateau

Method
Preheat the oven to 160C, 325F, gas mark 3. Grease and line a deep 9 inch round cake tin. Place the cocoa powder in a small heatproof bowl, slowly add boiling water, stiring until smooth. Whisk the eggs and caster sugar together until light and fluffy. Fold in cocoa mixture. Sift the flour and fold into the mixture. Pour into cake tin and bake in oven for 1 hour. Cool in tin for 5 minutes, then turn out onto a wire rack. When completely cool, peel off the paper and cut into 3 layers. Drain the mangoes, reserving the juice. Put one quarter of them in a blender and purée until smooth. Mix the cornflour with 3 tablespoons of the juice to form a paste. Add to mango purée. Transfer to a saucepan and heat, stirring until thick. Leave to cool. Chop the remaining mango. Whip the cream and reserve one quarter. Fold the chopped mango into the remaining cream and use to sandwich the layers of cake together. Place on a serving plate. Spread some of the reserved cream around the side of the cake and press the grated chocolate onto cream. Spread the mango purée over the top and decorate the Chocolate and Mango Gateau with piped cream.