Preheat your oven to 160ºC (325ºF) and line a 9-inch springform pan with parchment paper.

In a mixing bowl, combine crushed digestive or graham crackers with granulated sugar. Pour in melted butter and blend until it resembles wet sand. Press evenly into the bottom of the prepared pan and bake for 10 minutes. Let cool.

Toss fresh blueberries with granulated sugar, all-purpose flour, and lemon juice. In a separate bowl, mix flour and dark brown sugar for the crumble, then add melted butter until crumbly.

In a large bowl, beat full-fat cream cheese until smooth, then mix in granulated sugar, sour cream, and cornstarch. Add eggs one at a time, mixing until just incorporated.

Pour the cheesecake batter over the cooled crust, then spread the blueberry mixture evenly on top. Sprinkle the crumble over the blueberries.

Prepare a water bath by placing the filled pan inside a larger roasting pan. Pour hot water halfway up the sides of the springform pan and bake for 80-90 minutes until the center is slightly wobbly.

Turn off the oven and crack the door open, allowing the cheesecake to cool for 1 hour. Remove from the oven and let cool completely before refrigerating.

Cover with plastic wrap or foil and refrigerate for at least 6 hours, preferably overnight, before serving.