01 - Preheat oven to 350°F (175°C).
02 - In a large bowl, gently combine berries, granulated sugar, cornstarch, lemon juice, and vanilla until evenly coated.
03 - Transfer berry mixture into a lightly greased 8-inch square baking dish, spreading evenly.
04 - In a separate bowl, mix flour, oats, brown sugar, cinnamon, and salt. Add cold butter and blend using fingertips or a pastry cutter until the mixture resembles coarse crumbs.
05 - Sprinkle crumble topping evenly over berries.
06 - Bake for 35–40 minutes, until topping is golden brown and berry filling is bubbling.
07 - Allow to cool for 10–15 minutes before serving.