Prepare the apple filling by peeling and chopping 6 Granny Smith apples. Toss the apples in lemon juice, so they do not discolour. Melt 45 g (3 tablespoons)of butter in a frying pan and sauté the apples for about 5 minutes until soft. Leave to cool. Drain the apples of any liquid.
Whisk together brown sugar and cinnamon. Set aside.
In a small bowl, dissolve a packet of yeast in warm water and set to one side. Heat milk and butter in a saucepan until warm, about 110°F and pour into a large mixing bowl. Add to the bowl, sugar, salt and egg. To this mixture, add 240 g (2 cups) plain flour and mix until smooth. Give the yeast mixture a quick mix then add to the dough mixture. Then add the remaining flour.
Turn the dough onto a lightly floured surface and knead by hand for 5 - 10 minutes or until the dough is very smooth and elastic and no longer sticky. You could also knead the dough with a stand mixer fitted with a dough hook for 6-8 minutes.
Shape the dough into a ball and then put in a lightly oiled bowl. Cover with cling film and leave to rise in a warm place for 1 to 11/2 hours or until doubled in size. The best place to do this, is on the oven. Turn the oven on to 200°F. Heat for 2 minutes and then turn it off. Place your covered dough in the oven and leave it to rise.
Grease and line a 9 by 13 inch baking tin. Turn out the dough onto a lightly floured surface and knead gently for 1 minute. Roll out the dough into a rectangle 15 by 9 inches. Spread 30 g of softened butter over the dough leaving a 1 inch border all round. Sprinkle the buttered dough with cinnamon sugar mixture. Lightly press the cinnamon sugar into the butter.
Roll up starting from one long edge and press down to seal. Use a sharp knife and cut into 9 pieces. Arrange in the prepared tin. Cover with cling film and leave to proof in a warm place for 40 minutes.Preheat the oven to 190 °C. Bake the rolls in the preheated oven for 20 - 25 minutes, until well risen and golden in colour. Remove from oven and place on a cooling rack.