Make the Pastry: In a large mixing bowl, combine plain flour and sea salt. Add cubed chilled butter, mixing until resembling coarse breadcrumbs. Gradually add ice water, stirring until a dough forms. Chill for 1 hour.

Roll Out Pastry: After chilling, roll the dough to a ¼ inch thickness and transfer to a 7-inch pie dish. Trim and fold edges, refrigerate for 20 minutes.

Pre-bake Crust: Preheat oven to 220°C (425°F). Pierce the crust, line with baking paper, fill with beans, and bake for 20 minutes. Remove weighting and bake for another 10 minutes until golden.

Prepare the Filling: In a bowl, mix sliced peaches, blueberries, sugar, cornflour, and vanilla until combined. Set aside.

Make the Streusel: Combine rolled oats, additional flour, and sugar. Mix in softened butter until clumpy. Set aside.

Assemble the Pie: Fill the pre-baked crust with the fruit filling and sprinkle with the streusel topping.

Bake Pie: Lower oven to 180°C (350°F) and bake for 45 minutes until bubbling and golden.

Serve: Let cool completely, refrigerate for at least 3 hours before slicing. Serve with vanilla ice cream or cream.