Preheat the oven to 160°C (320°F) and line the base of a 20 cm springform pan with parchment paper. Grease the sides lightly.

Crush the digestive biscuits using a food processor or by smashing them in a zip-top bag with a rolling pin.

Melt 100 g of unsalted butter and combine it with the crushed biscuits, mixing until it resembles wet sand.

Press the mixture firmly into the base of the prepared pan and bake for 10 minutes. Set aside to cool.

In a small saucepan, combine blueberries, 50 g of granulated sugar, lemon juice, and cornstarch mixed with a splash of water. Cook over medium heat until thickened.

In a large bowl, beat cream cheese and 150 g of granulated sugar until smooth. Add eggs one at a time, mixing well after each addition.

Stir in vanilla and sour cream until well combined and creamy.

Make the crumble by mixing flour, oats, light brown sugar, and cold butter in a separate bowl, rubbing together until coarse crumbs form.

Pour half of the cheesecake filling over the cooled crust, and spoon half of the blueberry mixture over it, swirling with a knife.

Sprinkle half of the crumble topping over this layer. Repeat with the remaining filling, blueberry mixture, and crumble.

Bake for 45 to 55 minutes until the edges are set but the center is slightly wobbly.

Turn off the oven, leave the cheesecake inside with the door ajar for 1 hour, then transfer to the fridge to chill for at least 4 hours or overnight.