In a bowl, mix the flour, sugar, cornflour, yeast, cinnamon, and salt. Make a well in the centre and pour in the tepid milk, then add the soft margarine.
Bring everything together to form a soft dough and knead until smooth and bouncing back. This will take 5-10 minutes.
Cover and let the dough double in size which will take an hour or more.
Meanwhile, combine the cinnamon, sugar and margarine in a small bowl to make a paste.
Knock back and roll out the dough to a 24 by 30 cm rectangle. Spread the cinnamon sugar paste over the whole of the dough rectangle and then roll up to form a tight cylinder.
Cut the cylinder into 4 cm slices and place them on a lined baking sheet. Press down slightly, loosely cover and then leave to rise again for 30 minutes.
Preheat the oven to 180°C/350°F/gas mark 4. Bake the buns for 17-20 minutes until risen, golden and cooked through.
Meanwhile, melt the brown sugar into the water in a small saucepan. Bring to the boil and then turn off the heat. Brush the glaze over the top of the warm buns and then sprinkle with the pearl sugar (if using).
Remove the buns from the pans and let them cool completely on a wire rack.
If you like, combine the icing sugar with enough water to make a runny icing, then drizzle this over the buns before serving.