Preparation:
1. Preheat oven to 160°C (320°F) standard or 140°C (295°F) fan/convection.
2. Prepare a 20cm (8-inch) springform pan by lightly greasing and lining the base and sides with parchment paper, leaving an overhang for easy removal. Alternatively, lightly spray or butter the pan and line as needed.

Making the Biscuit Base:
1. Break biscuits into pieces and blitz in a food processor until fine crumbs form.
2. Add melted butter and pulse briefly until combined and resembling wet sand.
3. Press the mixture evenly into the base and up the sides of the springform pan using a flat tool.
4. (Optional) Bake the crust for 10–15 minutes at 175°C (350°F) until fragrant and edges turn golden, then let cool. This step firms the crust but is not mandatory. Refrigerate crust if not baking.

Making the Filling:
1. Beat cream cheese until smooth, about 20 seconds, avoiding over-aeration to prevent cracks.
2. Add flour and blend briefly until incorporated.
3. Add vanilla extract, sour cream, caster sugar, and lemon zest; beat until just combined.
4. Add eggs one at a time, mixing briefly after each until just combined. Avoid overmixing.
5. Pour filling into the biscuit crust.
6. Bake at 160°C (320°F) for about 55 minutes, or until the top is lightly golden, the cheesecake slightly jiggles in the center, and no cracks appear. Alternatively, bake at 175°C (350°F) for 15 minutes, then reduce temperature to 150°C (300°F) and bake for about 1 hour, followed by leaving the oven door closed and turned off for 1 hour to cool gradually (method helps prevent cracks).
7. Remove cheesecake from oven and cool gradually: first with the oven door slightly open about 8 inches for approximately 1 hour, then at room temperature.
8. Refrigerate for at least 4 to 6 hours, preferably overnight, to fully set.

Making the Strawberry Topping:
1. In a saucepan, combine diced strawberries, lemon juice or water, sugar, and vanilla extract.
2. Bring to a gentle simmer over medium heat and cook for about 10 minutes until strawberries soften.
3. Mix cornflour with 2 tablespoons water to form a slurry and whisk into the strawberry mixture.
4. Add halved strawberries and cook for an additional 1–2 minutes until the sauce thickens slightly.
5. Remove from heat; the sauce will thicken further as it cools. Adjust thickness by adding small amounts of water if necessary.
6. Cool to lukewarm, then spread the strawberry topping evenly over the cheesecake, placing strawberry halves facing down for presentation.
7. Refrigerate the assembled cheesecake for at least 2 hours before slicing and serving. The topping can also be prepared a day ahead for best flavor.