Preheat your oven to 350°F (175°C). In a large mixing bowl, gently toss the blackberries with sugar and lemon juice until well coated. Set aside to allow the berries to release some juice.
In another bowl, combine rolled oats, flour, cinnamon, and salt. Mix well to distribute the spices evenly.
Add the cold butter pieces to the dry ingredients. Use your fingers or a pastry cutter to work the butter into the mixture until it resembles coarse crumbs with some pea-sized pieces.
Spread the berry mixture evenly into a baking dish, making sure to include some of the juices for extra flavor.
Sprinkle the crumble topping evenly over the berries, covering them completely. The topping should look crumbly and slightly uneven for maximum crunch.
Bake in the preheated oven for about 25 minutes, or until the topping is golden brown and the filling is bubbling around the edges.
Remove from the oven and let the crisp rest for 10 minutes. This helps the juices thicken slightly and the topping to set with a satisfying crackle.
Serve warm, ideally with a scoop of vanilla ice cream or a dollop of whipped cream. Enjoy the contrast of crispy topping and juicy berries in every bite!
