In a standing mixer equipped with a dough hook, combine all the dough ingredients except the butter. Mix on low for 2-3 minutes until the mixture comes together. Gradually add the butter, one cube at a time, until fully incorporated. Continue mixing until the dough is glossy and can be stretched thin without tearing.
Place the dough in a lightly oiled container and leave it to prove until doubled in size, either in a warm spot or overnight in the fridge.
While the dough is proving, cream the butter and sugar together until light and fluffy, then whisk in the cinnamon.
Once the dough has risen, lightly knock it down and roll it out on a floured surface into a large rectangle, about 0.5-1cm thick.
Spread the filling evenly over the dough and roll it up into a tight scroll.
Slice the roll into nine even pieces and arrange them in muffin tins or a baking tray. Cover loosely with oiled cling film and leave to prove in a warm place until doubled in size, for approximately 1-2 hours.
Preheat your oven to 190°C (375°F), and then bake the buns for 14-16 minutes, or until golden brown. As soon as they come out, glaze with a simple sugar syrup and sprinkle with cinnamon sugar.