Preheat your oven to 160ºC (325ºF). In a food processor, blend 250 g of digestive biscuits with 3 tablespoons of granulated sugar until you achieve a fine, sand-like consistency. Pour in 145 g of melted butter, mixing until well combined. Press the mixture firmly into the bottom of a springform pan. Bake for 10 minutes until lightly golden and fragrant, then remove and allow to cool.

While the crust is cooling, toss 300 g of fresh blueberries in a bowl with 2 tablespoons of sugar, 2 tablespoons of flour, and 2 teaspoons of lemon juice until coated. For the crumble, combine 80 g of dark brown sugar, 60 g of flour, and 65 g of melted butter in another bowl. Mix until crumbly. Set both the blueberry mixture and crumble aside for later use.

In a large mixing bowl, blend 800 g of full-fat cream cheese with 3 tablespoons of granulated sugar until smooth and creamy, about 2-3 minutes. Slowly add 200 g of sour cream combined with 1.5 tablespoons of cornstarch, along with 2.5 teaspoons of vanilla extract. Finally, mix in 4 large eggs one at a time, ensuring the mixture is just combined for a creamy cheesecake texture.

Pour the silky cheesecake filling into the prepared crust, spreading it evenly. Scatter the blueberry mixture over the top, followed by the crumble topping. To prevent cracks, place the springform pan in a larger baking dish filled with hot water. Bake in the preheated oven for 1 hour and 20-30 minutes, until the edges are set while the center remains slightly wobbly.

Once the baking time is up, turn off the oven and let the cheesecake cool inside for 1 hour. Afterward, remove the cheesecake from the oven and cool it at room temperature for another hour. For the best flavor and texture, refrigerate the cheesecake for at least 6 hours, or ideally overnight, before slicing and serving your delicious Blueberry Crumble Cheesecake.