For the shortcrust:
1) Preheat the oven to 190C/Gas 5.
2) Place the flour, butter, and sour cream in a food processor and pulse to combine. When the dough has formed a ball, pat with lightly floured hands into the bottom and sides of an ungreased 25cm tart pan with a removable bottom and 1cm sides.
3) Bake for about 20 mins, until the pastry has set and only lightly browned if at all. Let cool while preparing the filling.
For the filling:
1) Preheat oven to 150C/Gas 2.
2) In a heavy-bottomed medium nonreactive saucepan, heat cream over medium-low heat for 15 mins, stirring to ensure it does not burn; do not let boil.
3) Add 60ml of double cream to beaten eggs. Mix together. Slowly add hot cream to mixture and add 100g sugar. Mix thoroughly.
4) Gently spread the blueberry preserves over the bottom of the baked and cooled tart shell, in a thin layer. Gently pour the custard over the preserves.
5) Bake for 40 mins or until the mixture is almost set in the centre (it should still wiggle when shaken). Let cool to room temperature and then refrigerate for at least 2 hrs, or up to 24 hrs.
6) Sprinkle the remaining 100g sugar in a thin, even layer over the baked custard filling. To caramelise the sugar, light a blowtorch and hold it so the flame just touches the surface. Start at the centre and spiral out toward the edges of the tart shell. If the sugar begins to burn, pull the torch away and blow on the sugar to extinguish the flame.
7) Top with sugared blueberries, pop out bottom of pan and serve.
For the sugared blueberries:
1) Lightly brush the blueberries with golden syrup and roll in sugar.