In a large bowl add the flour and sugar and rub in the butter to resemble fine crumbs.
Add the egg yolk and cream and form the paste into a ball.
Roll out the paste and line a 9” flan ring, then part bake the flan for 15 minutes.
Preparing the filling
Place a mixing bowl over a pan of boiling water and add 2 eggs, ½ tsp cinnamon, ½ cup sugar, ½ tsp vinegar and the salt.
Whisk until the mixture starts to foam and then remove the bowl from the top of the pan to a cool surface. Continue whisking until the mixture reaches the ribbon stage.
Pour onto the base of the flan and return to the oven until the filling has risen and is firm to the touch – about 15 minutes. Remove from the oven to a cooling rack and allow the filling to sink back into the shell. This is the first layer of the flan.
Melt the 6 ounces of chocolate and add the water and egg yolks. Whisk until combined.
Spoon half of the chocolate mix over the top of the sunken filling and return the flan to the oven for a further 5 minutes. Remove from the oven and allow the flan to cool completely. This is the second layer of the flan.
Beat the cream and cinnamon until stiff and carefully spread half of the mix into the flan. This is the third layer.
Fold the remaining cream and cinnamon and mix into the remaining chocolate mix and spread into the flan. This is the fourth layer. Sprinkle on the grated white chocolate.