In a large saucepan, add the berries, sugar, cornstarch, and lemon juice. Cook over medium heat for about 5 to 7 minutes. As the mixture heats up, you'll see the berries start to release their juices and the mixture will begin to thicken. Stir gently to combine, being careful not to break up the berries too much. Look for a glossy, syrupy consistency before removing the saucepan from heat.
Once the mixture has thickened, stir in the vanilla and a pinch of salt. Let the filling cool for at least 15 minutes.
While the filling cools, preheat your oven to 375 degrees Fahrenheit. On a floured surface, roll out the pie dough into a 12-inch disk.
Gently place the rolled-out dough into a 9-inch pie plate. Make sure to crimp the edges of the pie crust to give it that homemade touch.
Pour the cooled berry filling into the prepared pie crust. It’s okay if the filling is still warm.
For the crumble topping, combine the flour, brown sugar, white sugar, butter, cinnamon, and a pinch of salt in a mixing bowl. Using a pastry cutter or your fingers, mix until the mixture resembles coarse crumbs.
Sprinkle the crumble mixture evenly over the pie filling.
Place the pie in the oven and bake for 60 to 70 minutes. Check it at around 45 minutes to see if the top is browning too quickly; if so, cover it with foil to prevent burning.
After baking, remove the pie from the oven and let it cool completely.
Serve the pie warm or at room temperature.
