In a bowl, sieve the flour with the cocoa powder. In another bowl, cream together the butter, salt and icing sugar to obtain a light gloss cream. Add the egg yolks, flour and cocoa powder. Roll out to 3mm thick and freeze then cut into 2.5cm circles. Bake at 180°C/356F with 0% humidity for level 3 ventilation for 6-7 minutes. Set aside.
White chocolate and ginger cream
Finley grate the fresh ginger. Place the cream and ginger into a pan and bring to the boil. Remove from the heat, cover in cling film and infuse 10 minutes. Strain 300g if the infused mix into a saucepan and bring to the boil. Place the chocolate into a food processor and pour on the cream and emulsify. Allow to cool to 40ᵒc add in the butter and emulsify. Place in to piping bags.
Finish and assembly
To assemble the petits fours, pipe some white chocolate and ginger cream on to a chocolate biscuit and then place another chocolate biscuit on top.