Preheat your oven to 160ºC (325ºF). In a food processor, blend digestive or graham crackers with granulated sugar until finely crushed. Melt the butter and mix it with the crumbs until well combined. Firmly press this mixture into the bottom of a lined springform pan. Bake for 10 minutes or until lightly golden, then remove and let cool completely.

In a medium bowl, combine fresh blueberries, sugar, all-purpose flour, and lemon juice. Gently toss them to coat the blueberries evenly. For the crumble, in another bowl, mix flour and dark brown sugar, then add melted butter until crumbly. Set both mixtures aside.

In a large mixing bowl, beat full-fat cream cheese and granulated sugar with an electric mixer until smooth and creamy. In a separate bowl, whisk together sour cream and cornstarch until smooth, then add this to the cream cheese mixture along with vanilla extract. Mix until fully incorporated, then add eggs one at a time, blending until just combined.

Carefully pour the cream cheese filling into the baked crust, spreading it evenly. Gently layer the blueberry mixture over the filling. Sprinkle the crumble topping generously over the blueberries.

Prepare a water bath by placing the springform pan in a large roasting pan filled with hot water about halfway up the sides. Bake the cheesecake for 1 hour and 20-30 minutes, or until the center is slightly wobbly.

Once baked, turn off the oven and crack the door open slightly. Allow the cheesecake to cool for 1 hour in the oven. Transfer to the refrigerator and chill for at least 6 hours, or overnight, before slicing.