Preheat oven to 180°C (160°C fan bake). In a food processor, blitz the flour with the cold butter to make large breadcrumbs. Add the sour cream and blitz quickly to form a dough.
Tip the pastry out onto the surface, knead gently to bring it together. Bash the pastry on the surface a few times, this helps to stop shrinkage while baking. Flatten the pastry into a round, cling wrap and chill in the fridge for 30 minutes before rolling.
Allow the pastry 10 minutes out of the fridge. Roll between two sheets of greaseproof paper into a large circle about 5 cm larger than your dish.
With the remainder of the pastry, cut out strips or shapes to decorate the top.
Line your dish with pastry. Tip in the blueberry pie filling. Brush all the topping’s pastry with some beaten egg. Lay the strips on diagonally, spaced 1-2 cm apart. Repeat in the opposite direction.
Bake for 15-20 minutes until biscuit coloured. Remove and serve with cream or ice cream.