Crush the digestive or graham crackers and mix with granulated sugar and melted butter to form the crust. Press into the bottom of a springform pan.
In a bowl, combine fresh blueberries, sugar, flour, and lemon juice. Set aside to prepare the topping.
In a separate bowl, beat cream cheese and granulated sugar until smooth. Add sour cream, cornstarch, vanilla extract, and eggs, mixing until well combined.
Pour the cheesecake filling over the crust, then add the blueberry mixture on top.
Bake in a preheated oven until the edges are set but the center is slightly wobbly. Let cool before refrigerating.
Prepare the crumble topping by mixing flour, dark brown sugar, and cold butter until crumbly. Sprinkle over the blueberry layer.
Bake again until the crumble is golden brown. Allow to cool completely before serving.