Instructions:
- Preheat oven to 350°F (175°C). Wrap the outside of a 9-inch springform pan thoroughly with heavy-duty foil to ensure it is waterproof for the water bath.
- Make the Strawberry Reduction: Combine strawberries, 50g sugar, and lemon juice in a small saucepan. Simmer over medium heat until thickened (about 10-15 minutes). Cool completely.
- Prepare the Crust: Pulse biscuits until fine crumbs form. Mix with melted butter and 25g sugar. Press the mixture firmly and evenly into the base of the prepared pan. Chill in the refrigerator for at least 1 hour.
- Mix the Filling: Beat the softened cream cheese and 200g sugar on medium speed until perfectly smooth, ensuring no lumps remain. Beat in sour cream and vanilla.
- Add Eggs Gently: Beat in the eggs one at a time, mixing only until just combined after each addition. Gently fold in the cornstarch if using. Avoid over-mixing to prevent cracks.
- Assemble: Pour 2/3 of the cheesecake batter over the chilled crust. Dollop spoonfuls of the cooled strawberry reduction over the batter. Top with the remaining batter.
- Create the Swirl: Use a knife or skewer to gently marble the strawberry reduction through the batter with 3-4 sweeping motions. Do not over-swirl.
- Bake via Water Bath: Place the foil-wrapped springform pan inside a larger roasting pan. Carefully pour boiling water into the roasting pan until it reaches halfway up the sides of the cheesecake pan.
- Bake for 60–75 minutes. The edges should look set, but the centre 2 inches should still have a slight wobble.
- Cool Slowly: Turn off the oven, crack the door slightly, and leave the cheesecake inside for 1 hour. Remove from the water bath, unwrap the foil, and cool completely on a wire rack.
- Chill: Cover loosely and refrigerate for a minimum of 4 hours, or preferably overnight, before slicing and serving.