- In processor, pulse flour with salt. Add butter and pulse just until mixture resembles coarse crumbs with some pea-sized pieces of butter remaining (do not over mix). Drizzle 3 tbsp (45 mL) ice water over top. Pulse just until mixture comes together. Transfer to lightly floured surface and press into a disk (dough will be very crumbly; do not knead). Wrap and refrigerate at least 1 hr. After chilling, on lightly floured surface, roll dough into 13-in. (32-cm) round and line 9-in. (23-cm) pie plate. Trim and flute pastry edges. Prick all over with a fork or point of a sharp knife. Chill 15 to 30 min. until firm.
- Preheat oven to 425°F (220°C). Line pie shell with foil and pie weights. Bake 12 to 15 min., or until set. Remove foil and weights and bake another 5 min. until crust is lightly golden.
- Meanwhile, in bowl, toss blueberries, blackberries, cranberries and strawberries with the sugar, flour and lemon zest. Strain mixture to discard any accumulated liquid.
- To make topping, stir rolled oats with brown sugar and flour. Use fingertips to rub butter through mixture until crumbly; set aside. Scrape berry mixture into pie shell and sprinkle with crumble topping, leaving 1/4-in. (5-mm) border.
- Reduce heat to 375°F (190°C). Bake pie on middle rack, tenting with foil for 30 min. Remove foil and bake another 30 to 35 min., until crust and topping are golden brown and juices are bubbling. Transfer pie to wire rack to cool completely.
During baking, place foil-lined baking sheet on oven rack below pie to catch drips.