Method
Gently heat the milk, sugar and salt. Combine the flours and yeast in a stand mixer fitted with the dough hook. Pour in the milk, then the egg and knead for
one to two minutes, adding one to two tbsp flour if needed. Leave the dough in an oiled bowl in a warm place for one hour.
Roll the dough out to a large rectangle, one cm thick, with the short side facing you, then arrange the butter slices in the centre third, from left to right. Fold the left third of the dough over the butter, then right third of dough to enclose. Seal the edges. Turn the dough 90° clockwise and roll out to a 50 x 30 cm rectangle. Fold in three as before. Cover and chill for 15 minutes. Repeat three more times.
Roll the dough out to a 50 x 30cm rectangle. With the short side facing you, spread the puréed apples from top to bottom, in the centre third of the dough. Arrange the sliced apples on top. Mix the nuts and sugar together and set aside.
Cut the pastry either side of the filling into two-and-a-half cm-wide strips, leaving them attached at the centre, close to the filling. Brush the pastry with water, then plait the dough so that the filling is covered. Rest in a warm place for 30 minutes.
Preheat the oven to 180°C (350°F). Brush the pastry with egg wash, then sprinkle over the nut mix. Bake for 30 to 40 minutes until risen and golden. Cool.