3 tbsp plain flour
200g/7oz caster sugar
2 tsp vanilla extract
150驳/5陆辞锄 digestive biscuits
75驳/2陆辞锄 butter, plus extra for greasing
900g/2lb full-fat cream cheese
3 free-range eggs, plus 1 egg yolk, lightly beaten
200ml/7fl oz soured cream