1. MELT together the white chocolate and cream in a bowl over gently simmering water, stirring occasionally, until smooth. Stand ganache at room temperature for 2 hours before refrigerating until firm enough to pipe.
2. PLACE the butter, dark chocolate, sugar, cocoa, water and rum in a saucepan and melt together gently, stirring occasionally. Cool slightly.
3. WHISK in the sifted flours and then the egg and mix well. Transfer mixture to a jug and pour into 36 paper lined mini muffins pans.
4. BAKE in a moderate oven 180OC for 20 minutes or until cooked when tested. Stand 10 minutes before turning out onto a wire rack. Cool.
5. COLOUR the ganache with green food colouring to resemble leaves the spoon into a piping bag fitted with a 1cm star nozzle. Pipe a rosette of ganache onto each cake to resemble a tree then decorate. Store in an airtight container in the refrigerator until required.