Preheat the oven to gas 612, 210 degrees Celsius, fan 190 degrees Celsius. Toss the apples with the dates, cinnamon, sugar, lemon zest, and juice in a mixing dish. Combine the walnuts and cornflour in a mixing bowl.
The dough should be rolled out to the thickness of a pound coin. Place on a baking sheet lined with parchment paper. Place the apple mixture in the center of the plate.
Cut the dough into 3cm strips on both sides with a knife. To construct a plait, cross alternate strips over the filler, overlapping them. Sprinkle with demerara sugar after brushing with beaten egg. Preheat oven to 350°F and bake for 30 minutes, or until golden brown.