Dust a surface with flour and roll out your pastry to a bit bigger than an 8 1/2-by-11-inch sheet of paper. Brush with the egg yolk and scatter the rest of the ingredients over, being subtle with the allspice and cinnamon. Roll the pastry up tightly like a Swiss roll to make a long sausage shape. With a knife, cut across the sausage into 1-inch (2 1/2-centimeter) pieces. Take 8 pieces aside, and freeze the rest of the pastry for a rainy day.
Preheat the oven to 400 degrees F (200 degrees C/gas 6).
Turn all the pieces of pastry swirl-side up and flatten them slightly. Dust the surface of your pastry with flour, then roll each piece out into a thin circle (around the size of a teacup saucer). Even I don't have proper pastry molds at home, so I just grease and flour the outsides of 8 of my glass tumblers. Then, I place a circle of pastry on top of each tumbler, pleating, pinching and hugging the pastry around them.
Place the tumblers on a baking tray, pastry at the top, and put in the preheated oven until crisp and golden, around 15 minutes. Remove from the oven and, while still hot, take a tea towel and pat the slightly raised top of the pastry back down on to the flat bottom of the tumbler ? giving you a flat base again. Allow to cool, and carefully remove the pastry cases from around the tumblers.
Fill your pastry cases with the chocolate filling: Place the double cream, sugar, and pinch of salt in a pan and bring to the boil. As soon as the mixture has boiled, remove from the heat, and add the butter and chocolate. Stir until it has completely melted. Allow the mixture to cool slightly, stirring in the cold milk until smooth and shiny. Sometimes this mixture looks like it has split. Allow the mixture to cool down a bit more, and whisk in a little extra cold milk until smooth. Scrape all the mixture into the cooked pastry shells. Shake to even it out and allow to cool for around 1 to 2 hours, until it is at room temperature. Dust with the cocoa powder. Ultimately the pastry should be short and crisp and the filling should be smooth and should cut like butter.