Roll out the dough until you have a rectangle of around 37cm x 52cm (have the shorter side facing you).
Spread the butter evenly over the dough, leaving a narrow edge (around 1cm) all the way round.
Combine the sugars and cinnamon and sprinkle over the butter, using your fingers to evenly distributed the mixture.
Carefully begin to roll up the dough, pulling it fairly taut as you roll.
Place the dough, seam side down, and cut into 12 rolls.
Pop the rolls on a lined baking tray or in a greased tin, allowing for a little space in between. Cover the dish or tray with a tea-towel.
If baking immediately: pre-heat the oven to 200°C / 400℃. Cover the buns with a tea-towel, and leave them to rest for around 30 minutes.
Overnight buns: cover the buns with clingfilm and place in the fridge. In the morning, pre-heat the oven to 200°C / 400℃ and allow the buns to come up to room temperature (I usually sit the dish on top of my oven as it's heating up).
When ready to bake, sprinkle with the chocolate chunks.
Bake for around 20-25 minutes.