Use a 28-cm spring-form tin. Sift flour and baking powder into a large bowl. Make a well in the centre; place the sugar, eggs and butter in it. Using the fingertips of one hand, draw all the ingredients in the centre together, then draw in flour from the edge to make a soft dough. Knead well and gather into a smooth ball. Wrap in cling wrap and chill for 30 minutes.
Preheat oven to 200°C. Peel, halve and core apples. Remove grape stems. Combine the apples, grapes, white wine, sugar and cinnamon in a pan. Simmer gently over medium heat for 5 minutes. Leave to cool for a few minutes.
Roll out two-thirds of the dough on a floured surface. Grease tin. Line with pastry, shaping an edge about 2.5 cm high. Prick base several times with a fork. Bake for 10 minutes.
Spread fruit mixture on pastry base. Roll out remaining pastry and place on top of filling. Brush with egg yolk and bake 25 minutes. Leave to cool. Mix lemon juice and icing sugar together to make a fairly runny consistency. Drizzle over pie.