1 For the cake: heat the oven to 180°C (160° fan) 350°F gas 4. Grease and line a 23cm x 30cm|9" x 12" baking tin.
2 Mix the cocoa with the boiling water. Stir in the bicarbonate of soda and set aside to cool.
3 Whisk the eggs, sugar, oil and vanilla in a mixing bowl until blended. Stir in the flour and the cocoa mixutre until smooth.
4 Pour into the tin and bake for 30-40 minutes until risen and firm to the touch. Cool in the tin for 10 minutes, then turn out onto a wire rack to cool.
5 for the decoration: melt the chocolate with the cream in a heatproof bowl over a pan of simmering (not boiling) water. Stir until smooth and spread over the cool cake.
6 Scatter with the sprinkles and chocolate beans and leave to set.