1. Preheat the oven to 300°F (150°C). Butter a 9in (23cm) springform pan. Grate the zest from the lemons and squeeze 4 tbsp lemon juice. Process the cottage cheese, cream cheese, sour cream, sugar, cornstarch, and 3 tbsp lemon juice in a food processor until smooth. Add the eggs and process to combine. Stir in the poppy seeds and transfer to the pan.

2. Bake for 1½ hours, or until the sides of the cheesecake are beginning to brown.

3. To make the berry sauce, purée the berries, sugar, and remaining 1 tbsp lemon juice in a food processor. Cover and refrigerate.

4. Transfer the cheesecake to a wire cake pan. Run a knife around the inside of the pan. Cool completely in the pan. Cover and refrigerate at least 5 hours, until chilled. Remove the sides of the pan, slice, and serve, with the berry purèe.