Place milk, yeast and caster sugar in a small jug and whisk to combine. Set aside for 5 minutes or until frothy.
Using an electric mixer with a dough hook attachment, knead flour, salt flakes, eggs and yeast mixture in a large bowl for 2 minutes or until just combined. Add butter, 1 cube at a time, kneading between additions. Knead for 5 minutes or until dough is smooth and elastic. Place in a lightly greased bowl, cover with a clean tea towel and set aside in a warm place for 1 hour or until nearly doubled in size.
Preheat oven to 190°C/170°C fan-forced. Grease and line a 11 x 21cm (7cm deep) loaf pan with baking paper, extending paper 2cm above edges. Roll dough out on a lightly floured surface to form a 30 x 50cm rectangle.
To make the cinnamon paste, combine all the ingredients together in a small bowl. Spread mixture evenly over dough, then top with apple. Cut dough lengthways into thirds, then cut each strip into quarters. Place 3 dough pieces on top of each other to create 1 stack. Repeat to create a total of 4 stacks. Transfer stacks, cut-sides up, to pan. Bake for 40 minutes, covering with foil if over-browning, or until golden brown on top and a skewer inserted into centre comes out clean. Stand in pan for 10 minutes, then transfer to a chopping board to cool slightly.
To make the glaze, stir icing sugar and milk in a small bowl until smooth. Drizzle icing over loaf. Serve warm.