Preheat the oven to 160°C (140°C fan) or 320°F. Mix crushed digestive biscuits with melted butter and press into a greased springform tin. Chill in the fridge.
Make the Cheesecake Filling: Beat cream cheese, sugar, and vanilla until smooth. Add eggs one at a time, then fold in sour cream.
Bake the Cheesecake: Pour the filling over the base and smooth the top. Bake for 50-60 minutes until set but slightly wobbly in the center. Turn off the oven, crack the door open, and let it cool gradually. Refrigerate for at least 4 hours or overnight.
Prepare the Berry Topping: Cook mixed berries, sugar, and lemon juice over medium heat for 5-7 minutes until thickened. Let cool.
Make the Crumble Topping: Rub cold butter into flour until crumbly, then mix in sugar. Bake at 180°C (160°C fan) or 350°F for 15 minutes until golden. Cool completely.
Assemble: Spread the berry topping over the cheesecake, sprinkle with crumble