Preheat the oven to 200°C.
Pulse flour and butter in a food processor until breadcrumbs form.
Mix in sugar, egg, and 1-2 tablespoons of water to form a smooth dough.
Roll dough to 3mm thick, line the tart tin, prick the base, and chill for 15 minutes.
Blind bake with beans for 12-15 minutes at 200°C, then 8-10 minutes at 160°C without beans.
Simmer apples, sugar, and water in a lidded pan for 5-10 minutes until softened.
Stir in blackberries and simmer for another 5-10 minutes until tender.
Rub crumble ingredients together until small clumps form.
Strain fruit juices into a bowl and spoon the fruit into the pastry case.
Top with crumble and bake at 200°C for 20-25 minutes until golden.
Boil the reserved fruit juice for 3-4 minutes until it becomes a syrup.
Serve warm with the fruit syrup and cream or custard.