Preheat your oven to 160ºC (325ºF) and prepare a 23 cm (9 inch) springform pan by lining the bottom with parchment paper.

In a food processor, blend the digestive or graham cracker crumbs with granulated sugar. Melt the butter and mix it in, then press into the bottom of the prepared pan. Bake for 10 minutes and let cool.

Gently toss fresh blueberries with sugar, all-purpose flour, and lemon juice in a small bowl. Set aside.

Mix all-purpose flour and dark brown sugar in a separate bowl, then add melted butter until the mixture resembles coarse crumbs.

Beat softened cream cheese in a mixer until smooth. Gradually add granulated sugar, then sour cream, cornstarch, and vanilla extract. Add eggs one at a time.

Pour the cheesecake batter into the cooled crust, layer the blueberry mixture on top, and sprinkle the crumble topping.

Place the springform pan into a larger baking dish filled with hot water. Bake for 80-90 minutes until slightly wobbly in the center.

Cool the cheesecake in the oven with the door ajar for 1 hour, then transfer to a wire rack until room temperature. Refrigerate for at least 6 hours before serving.