Preheat oven to 200°C. Line 2 baking trays with paper.
Roll pastry into a large rectangle and then cut in half lengthwise. OR cut commercial puff pastry sheets in half and set aside.
Make a béchamel sauce by placing egg and egg yolk, crème fraiche, butter, cornflour and milk into the Thermomix bowl. Cook 6 min/100°C/speed 4. Cool.
Lay cheese and ham slices across 1 half of each pastry sheet leaving room around the edges to seal. Top with béchamel and cover with other half of pastry. Seal borders with a fork or small knife. Slash tops to allow steam to escape and brush liberally with egg wash. Bake for 20–25 minutes until puffed and golden. Serve hot.