Preheat the oven to 350 °F
Mix together the blueberries, ½ brown sugar, 2 tablespoons of cornstarch and 1 tablespoon of lemon juice and pour the mixture into an 8x8-inch baking dish or 10-inch round pie dish
Mix together the ingredients for the crumble topping and sprinkle evenly over the blueberry mixture.
Bake for about 30-35 minutes, or until the topping has turned golden-brown.