Place the blueberries and cinnamon sticks in a small saucepan and add ½ dl. apple cider and ½ dl. sugar. Heat carefully and stir until the sugar has dissolved. Place on one side.
Place the sour cream in a bowl and whisk until it stiffens. Whisk the cream in a separate bowl.
Place the egg yolks, apple cider vinegar and the rest of the cider and sugar in a metal or glass bowl and whisk in a bain-marie until the mixture is light and airy. Then gradually fold this mixture into the whipped sour cream and then fold in the whipped cream. The reason for doing this in stages is so that you retain the airiness.
Pour the mixture into a suitable tin, i.e. a tin that can be placed in the freezer.
Pour over the blueberry syrup and spread it over the top. Some of the berries will sink down into the airy mixture, creating a lovely pattern. You might like to run the tip of a knife across in order to obtain an even more dramatic pattern in the blueberry mixture.
Cover with cling film and place the tin in the freezer until the mixture freezes, preferably overnight. Allow to stand at room temperature for 10 to 15 minutes before serving.