Mix the butter with the biscuits and cinnamon; spoon into the base of a 23cm loose-based flan tin and press down well; chill
Sprinkle the gelatine over the cold water; leave to soften for 5 minutes then place the bowl in the microwave for a few seconds and stir to dissolve
Whisk the egg yolks and sugar until thick; put the chocolate in a bowl with the coffee and stir until melted; add to the egg mixture, then cook gently in a pan, stirring constantly for 1-2 minutes until thickened; stir in the gelatine; leave until just beginning to set, stirring occasionally
Whip 225ml of the cream until soft peaks form; whisk the egg whites until stiff; fold the cream into the coffee mixture followed by the egg whites; pour the mixture over the biscuit base and chill for 2 hours
To serve remove from the tin and transfer to a serving plate; whip the rest of the cream and dollop it on top; decorate with grated chocolate and cinnamon
8 servings