Preheat your oven to 160ºC (325ºF). In a mixing bowl, combine crushed digestive or graham crackers with granulated sugar, then pour in melted butter. Mix thoroughly until the texture is similar to wet sand. Firmly press this mixture into the bottom of a springform pan. Bake for 10 minutes until set, and let it cool completely.

While the crust cools, toss fresh blueberries with granulated sugar, all-purpose flour, and lemon juice in a bowl. Mix all-purpose flour and dark brown sugar in another bowl, then drizzle in melted butter, combining until it resembles coarse crumbs.

Beat room-temperature cream cheese until smooth; gradually add granulated sugar. In a separate bowl, whisk sour cream and cornstarch, then add this mixture along with vanilla extract to the cream cheese blend. Incorporate eggs two at a time, mixing just until smooth.

Pour the cheesecake filling over the cooled crust, distribute the blueberries on top, and sprinkle the crumble mixture over the blueberries. Place the springform pan into a larger baking dish filled with hot water and bake for 1 hour and 20-30 minutes.

Turn off the oven and leave the cheesecake inside for about 1 hour. Once cooled, carefully remove the cheesecake from the oven and chill in the refrigerator for at least 6 hours before slicing.