Put half of the chocolate chips, hazelnuts, and plain flour in the bowl of a food processor. pulse until the hazelnuts are coarsely chopped. Pour the hazelnut mixture into a small bowl and set aside.
Combine remaining chocolate chips and granulated sugar in the food processor. Blend until the mixture is finely ground. With the machine running, gradually add the hot water until the chocolate is melted and mixture is smooth.
Add the eggs, butter, vanilla and cinnamon. Pulse until mixture is blended. Return the hazelnut mixture to the food processor and pulse to incorporate.
Pour the mixture into a buttered and plain floured 22-cm pie dish. Bake for 35 minutes. Place the pie on a cooling rack and cool for one hour. (The top may crack during cooling, don't worry.)
Once cooled, refrigerate for 2 hours. (The pie can be made 1 day in advance and stored in the refrigerator). Allow the pie to return to room temperature for 30 minutes before serving.
In a large mixing bowl, whip the cream until it forms soft peaks. Add the sugar, vanilla, and cinnamon and continue to beat until cream holds stiff peaks.
To serve: cut the pie into slices and top with a dollop of the vanilla cream.