For the cheesecake, preheat the oven to 180C/350F/Gas 4.
Place the sponge base into the bottom of a 23cm/9in springform, loose-based cake tin.
Place the sugar, lemon juice and zest and cornflour into a bowl and whisk together.
Add the cream cheese and beat well. Crack in the eggs, one at a time, beating well between each addition. Add the vanilla seeds and mix well, then pour in the double cream and whisk until the mixture is smooth. Fold in the strawberries and white chocolate.
Pour the mixture into the cake tin and give the tin a light shake to evenly distribute the mixture.
Wrap the cake tin in a sheet of foil to make it waterproof, then place it into a roasting tin filled to a depth of about 0.5cm/¼in with water. Transfer to the oven and bake for 50 minutes, or until the top is lightly golden-brown and the cheesecake is just set. Remove from the oven and leave to cool in the tin, then keep in the fridge until ready to serve.
For the strawberry sauce, heat a frying pan until hot and place 250g/8oz of the strawberries into the pan. Stir-fry for one minute.
Stir in the lemon juice and icing sugar, to taste.
Pour the mixture into a blender and blend until smooth, then pass through a sieve, pressing with the back of a spoon, to remove all the seeds.
To serve, remove the cheesecake from the fridge, remove from the tin and place a slice onto a serving plate. Top with the sauce and some strawberries.