Preheat oven to 210 degrees (fan-forced). Lightly grease a 20cm round cake tin and set aside.
Sift flour into a bowl. Rub in the butter in using your fingertips.
Add the milk and mix to a soft dough. Knead on floured surface until smooth.
Roll the dough out into a 5mm thick rectangle.
Place the butter (softened to room temperature), brown sugar and cinnamon into a bowl. Mix with a spoon until creamy and smooth.
Spread the cinnamon butter mixture onto the dough. Sprinkle over the chopped apple.
Gently roll the dough up into a tube (lengthways). Use a sharp knife to cut the roll into 8-12 pieces.
Place the pieces cut side up into the prepared cake tin (allow the rolls to touch one another as this will help them to rise).
Bake for 15 minutes or until golden brown. Allow to cool slightly in the tin.
Place the icing sugar and 2 tbs hot water into a bowl. Mix until a smooth paste forms. Use a spoon to drizzle over the buns. Note: If the mixture is still too thick, add another tablespoon of hot water and mix for a further 10 seconds. Serve warm or cold.