Prepare pie crust recipe, if making your own, and chill in fridge for at least one hour.

To make crumble topping, combine flour, brown sugar, granulated sugar, and cold cubed butter in a bowl. Use a pastry blender or a fork to work butter in until the mixture resembles coarse crumbs. Cover and chill in refrigerator one hour.

To make filling, add strawberries, blueberries, lemon juice, cornstarch, sugar, cinnamon, and butter in a medium saucepan. Add water if using fresh berries. Heat over medium-high heat until it reaches a simmer.

Reduce heat to low and simmer for 5 minutes or until mixture is thickened. Remove from heat and stir in vanilla. Set aside.

Preheat oven to 425℉.

To blind bake your pie crust, roll out pie crust on a floured surface to a 13-inch round. With floured hands, gently fold pie crust in quarters to transport it to your pie pan.

Press pie dough into pie pan and crimp sides, letting the edges extend a bit beyond the edge of the pan.

Line the bottom of your pie pan with parchment paper and fill it with pie weights or uncooked rice. Bake pie crust in preheated oven for 15-20 minutes or until the edges of the crust are starting to turn lightly golden brown.

Remove from the oven and let cool slightly. Reduce oven heat to 375℉.

To assemble your pie, dust the inside of blind-baked pie crust with "crust dust" (see note), and pour filling evenly into crust.

Top with crumble topping. Bake in preheated oven for 40 minutes or until crumb topping is golden brown and filling is bubbling (if pie begins to brown too much, cover it loosely with aluminum foil.

Allow baked pie to cool completely before slicing.