Sift the flours into a pile on a clean work surface. Make a well in the centre and add the butter, sugar and egg yolk. Gradually work into the flour with your fingertips until the mixture comes together to form a soft dough. Cover with clingfilm and chill for 30 minutes until firm.
Dust the work surface with a little flour and roll out the dough to a thickness of 5 millimetres. Cut into discs with a 4 centimetre round cutter and transfer to a baking sheet lined with greaseproof paper. Refrigerate for 30 minutes until firm. For the biscuits preheat the oven to 150°C. Bake the biscuits for 25 to 30 minutes until a pale gold colour then transfer to a wire rack to cool.
Mix the cream cheese, icing sugar and vanilla extract together until smooth. Spread half of the biscuits with the cream cheese mixture and spoon a small amount of jam into the middle. Sandwich with the remaining plain biscuits. Pour the ingredients for the smoothie, except the digestives, into a liquidiser and blend until smooth. Divide between chilled serving glasses and top with the crushed biscuits. Unwrap the straws and cut to length with a hot knife. Serve the smoothies with the cheesecake biscuits.