Grease a skillet with butter. Place the berries in the skillet and drizzle with lemon juice. In a small bowl, whisk together the sugar and cornstarch. Sprinkle the mixture over the berries.
PREPARE THE TOPPING:
In a medium bowl, combine the flour, brown sugar, cinnamon and salt. Using a pastry blender or two knives, cut in the cold butter until pea-sized pieces form. Using your fingertips, mash the mixture together to form large clumps. Sprinkle the mixture evenly over the berries.
Bake in the preheated oven for 45 to 60 minutes or until the topping is golden brown and the filling is bubbling.
Remove the skillet from the oven and place on a wire rack. Let cool for 15 minutes. Spoon the crumble into individual serving bowls and top with vanilla ice cream.