Break the chocolate into pieces and place in a bowl. Set aside.
Place the milk and the cream in a pan and bring to the boil.
Beat the egg yolks with the sugar until you obtain a light, fluffy mixture.
Once boiling, pour the milk and cream over the egg yolks and then return to the pan and the heat. Stir constantly until the liquid thickens and coats the back of your spoon. If you have a thermometer, heat to 84'C.
Once cooked, pass the liquid through a sieve onto the broken chocolate. Stir gently until the chocolate has melted and is fully incorporated into the mixture.
Pour the chocolate cream into glasses and then place in the fridge to set for at least 45 minutes.
Preheat the oven to 200°C (Gas mark 6-7).
Mix the flour, butter, salt and icing sugar together until it forms a ball.
Place between 2 sheets of baking parchment and roll to a thickness of 5mm. Remove the paper, place on a baking sheet and bake for 15 to 20 minutes.
Once golden brown, use a pastry cutter or an upturned glass to cut the shortbread into rounds and dust with caster sugar.
Pour the double cream and espresso coffee into a syphon. Add the icing sugar and then screw the lid firmly shut. Charge the syphon with gas and then shake vigorously.
To serve: Squirt some of the emusion on top of the cream, sprinkle on some chopped pistachios and finish with the shortbread biscuit.
«To vary the flavours of this dessert, add some brandy or orange zest to the emulsion.»