To make the pastry, sift white and wholemeal flours and the spice into a bowl; tip in the bran left in the sieve. Rub in the butter until the mixture resembles fine breadcrumbs. Stir in sugar.
Mix the egg yolk with 1 tablespoon cold water. Add to the flour mixture and mix to form a soft dough, adding a few drops more water, if needed. Gather dough into a small ball; wrap in cling wrap and chill for at least 30 minutes.
Preheat oven to 190 degrees C. Peel and slice the apples and mix with blueberries. Combine the sugar, cinnamon and nutmeg. Reserve 1 tablespoon and stir the rest into the fruit.
Roll out dough on a non-stick baking sheet to make a 30cm round and brush all over with some of the egg white.
Pile fruit mixture in the middle of the pastry, then draw the edges up over the fruit, leaving the centre open. Brush case with the remaining egg white and sprinkle with the reserved spiced sugar.
Bake for 30–35 minutes or until the pastry is golden brown and the apples are tender. Serve warm with vanilla yogurt.