Preheat your oven to 160ºC (325ºF). In a food processor, blend digestive or graham crackers with granulated sugar until finely crushed. Melt butter and combine it with the crumb mixture, then press firmly into the bottom of a 9-inch springform pan. Bake the crust for 10 minutes until golden, then cool completely.

In a medium bowl, gently mix fresh blueberries with granulated sugar, flour, and lemon juice until coated. Set aside. For the crumble, combine flour and dark brown sugar in a separate bowl. Melt butter, add to the mixture, and mix until crumbly; set aside with the blueberries.

In a large mixing bowl, beat cream cheese until smooth. Gradually add sugar, mixing until well-combined. Blend in sour cream and cornstarch. Add room temperature eggs one at a time, mixing gently to avoid excess air.

Pour the cheesecake filling into the cooled crust. Evenly distribute the blueberry mixture over the filling. Sprinkle crumble topping generously over the blueberries.

Place the springform pan inside a larger baking dish filled with hot water and bake for 1 hour and 20-30 minutes until the center is slightly wobbly. Turn off the oven and leave the cheesecake inside with the door ajar for 1 hour to cool.

Transfer the cheesecake to the fridge. Chill for at least 6 hours or overnight. Release the springform pan, slice, and enjoy.