In a bowl, whisk the butter and icing sugar until fluffy and then whisk in the egg yolk.
Mix together the flour, cocoa, vanilla sugar and cinnamon in a separate bowl, and then fold into the butter mixture.
Work together to a dough and cover in plastic film. Refrigerate for about 20 minutes.
Set the oven temperature to 180 °C.
Divide the dough into 20 pieces and press into small foil cases, prick with a fork and bake in the oven for 10 minutes. Leave to cool.
Meanwhile make the caramel filling. Heat the cream, butter and vanilla sugar in a saucepan. Put aside and bring the glucose syrup, salt and sugar to 120 °C in another saucepan, stirring occasionally.
Carefully pour the cream mixture into the syrup mixture and heat to 124 °C, stirring occasionally.
Pour the filling into the cases and leave to cool at room temperature.
Chop the chocolate. Bring the cream to the boil. Pour the warm cream over the chopped chocolate and stir to a smooth mixture. Refrigerate for at least 20 minutes to cool.
Spread the ganache on the caramel filling and sprinkle with salt flakes. Place in the refrigerator. Remove the tarts a little while before serving.
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