Grease 4 x 12cm diameter, fluted tart tins and set aside (note 1). Weigh the flour, butter, cocoa powder, sugar and salt into the bowl of a food processor with the blade attachment fitted and process well combined. Add the egg and process on high until the pastry begins to clump together, it will look a bit like dark, sandy soil.

Turn the pastry out onto the benchtop and knead briefly until it forms a soft, pliable dough. Roll out between two sheets of clingfilm until it is 3mm thick - about the thickness of a heavy coin. Cut out two circles large enough to line the tart tins, and press them gently, but firmly into two of the prepared tins. Run your rolling pin over the top to the tart tins to trim the pastry, then stack up all the remaining pieces and re-roll them. Cut out another circle (two if possible) and repeat until all the tins are lined with pastry. Chill in the freezer 15-30 minutes.

Heat the oven to 200°C / 400° F / Gas 6. When the pastry cases have chilled, remove from the freezer and line with a layer of baking paper followed by a layer of tin foil (see pictures). It helps to scrunch up the paper so that it fits neatly into the tins. Place on a baking tray and blind bake in the preheated oven for 15 minutes. Carefully remove the paper and foil, then bake another 5 minutes. Remove from the oven and set aside to cool.

To make the raspberry puree, gently heat the berries, lemon juice and sugar in a small saucepan. Use a fork to squash the berries until they release their juices, then bring to a simmer. Simmer, stirring for 1-2 minutes until the mixture begins to thicken. Strain through a sieve, pressing with the back of a spoon to extract as much puree as possible. Discard the seeds.

To make the filling soak the gelatine in a small dish of cold water for 5 minutes until softened. Heat the milk in a small saucepan until warm but not boiling (this happens quickly!) then squeeze all the liquid out of the gelatine sheets and stir into the hot milk until dissolved. Remove from the heat and set aside.

Stir together the cream cheese, sour cream, sugar, vanilla extract and lemon zest until well combined. Pour in the warm milk mixture and stir well to mix through.

Spoon 2-3 teaspoons of the puree into the base of each pastry case, then divide the creamy filling between each. Spoon more puree on top of the tarts and use the handle of a teaspoon or a fork to ripple the puree through the filling. Chill for 1-2 hours before serving.

To serve, remove from the fridge 15 minutes before you are ready to eat, top with extra berries, mint leaves and a sprinkle of icing sugar.