Combine the flour, cornflour, cream of tartar powder and salt in a mixing bowl. Add the chilled butter and rub together until the mixture resembles coarse breadcrumbs. Add the sugar and vanilla seeds. Mix the egg yolks with 3 tablespoons cold water and add to the mixture. Combine everything to a smooth dough. Set aside 320 g (11¼ oz) of the dough.
Dust your benchtop with flour and roll out the remaining dough to a circle about 30 cm (12 inches) in diameter and 5 mm (¼ inch) thick. Line the buttered pie pan with the dough. Trim off any excess and add it to the remaining dough. Cover the remaining dough with cling wrap and refrigerate. Refrigerate the pie pan with the dough lining for 25 minutes. Preheat the oven to 175°C (330°F/Gas mark 4-5).
Meanwhile, peel, core and dice the apples. Combine them with the lemon juice in a bowl. Chop the cranberries and walnuts and add to the apple mixture. Set aside.
Line the pie base with baking paper and top with dry beans. Blind bake the base for 20 minutes, then remove the baking paper and beans. Continue to bake for another 10 minutes. Leave to cool.
Whisk together the eggs, egg yolk, honey, flour, crème fraîche and vanilla seeds. Combine with the apples and arrange the mixture on top of the pie base in a dome shape. Brush the pie base edges with a little egg.
Dust your benchtop with flour and roll out the remaining dough to a circle about 27 cm (10¾ inches) in diameter and 5 mm (¼ inch) thick. Slice into strips about 1.5 cm (5/8 inch) wide. Carefully arrange the strips on top of the filling to form a lattice. Trim off excess dough. Brush the dough with the remaining egg and generously sprinkle with sugar. Bake the apple pie in the preheated oven for about 75 minutes. Cover with aluminium foil after about 35 minutes.