Preheat oven to 400°F (200°C).

1. On a lightly floured surface, roll out dough into a circle large enough to fit pie plate, dusting work surface and dough as necessary to keep the dough from sticking (or roll between 2 pieces of waxed or parchment paper). Press dough into prepared pie plate, crimping edge. Place pie plate in freezer or refrigerator for 15 to 20 minutes to chill while you prepare the filling.

2. Filling: In a large bowl, gently combine raspberries, blackberries, sugar, cornstarch, lemon juice and cinnamon, making sure that cornstarch is not lumpy. Transfer filling to prepared bottom crust. Place pie plate on baking sheet and bake in preheated oven for 45 minutes.

3. Remove from oven, reduce temperature to 350°F (180°C) and sprinkle streusel over pie, avoiding juicy edge. Return pie to oven and continue baking for 15 minutes more or until nicely browned and juices are bubbling and thickened around edge. If pie starts to get too brown before it’s finished baking, cover loosely with a piece of tented foil. Let cool on a wire rack for 1 to 2 hours before serving.