1. Sieve the flour and cocoa powder together.
   
2. In a bowl, work the sugar and butter with a wooden spoon to a thick cream.  Add the salt, coffee and egg.  Mix well, then add the flour/cocoa mixture.  Knead for a couple of minutes and form a ball.  
   Place the pastry dough between two sheets of baking parchment, flatten a little with your hand, then roll out using a rolling pin to a thickness of 3 mm.  Roll in both directions so that the dough is of an even thickness.  Slide everything onto a baking sheet and refrigerate for 1 to 2 hours.  The pastry should be left refrigerated long enough to harden so that the biscuits don’t stick. 
   
3. Preparation of the ganache:
   Grate the white chocolate into a bowl, add the crème fraîche, and melt over a bain-marie.  When the chocolate has melted, mix with a wooden spoon, then allow to cool to room temperature.  
4. Preheat the oven to 165°.
   
5. Remove the pastry from the fridge and carefully life off the upper sheet of baking parchment. Using a biscuit cutter diameter 6 cm , cut out the biscuits and place on to another baking tray covered with baking parchment.  Cut out a 3 cm hole from half of the biscuits with the end of a metal lid.
   
6. Bake for 15 minutes.  Remove from the oven and allow to cool.
7. Once cooled, spread the whole biscuits with a teaspoon of white chocolate ganache, then place the biscuits with the hole on top. 
   
8. Allow to cool for at least an hour. 
   
   

These biscuits will keep up to 15 days in a tin.