Put the warmed (not hot!) milk in a small bowl with the sugar and yeast. Whisk together and set aside for 5 mins.
Add the egg and the melted (not hot!) butter. Whisk.
Put the 370g/13oz flour in a large bowl with the salt. Whisk together and make a well.
Pour in the milk mixture. Stir until all the flour is incorporated into a sticky dough. Cover the bowl and rest for 5 minutes.
Lightly dust your surface. Tip the dough onto the surface. Sprinkle the 30g/1oz of flour on top.
Knead for about 5 minutes. It will be sticky at first but keep going and it will start to become easier to work with until you have a smooth, springy ball of dough.
Clean and oil the bowl, pop the dough into it, rub the top with a touch of oil, then cover the bowl and leave in a warm place for 1 hour.
Make the cinnamon chocolate butter
Put the butter in a small bowl with the sugar, cinnamon and cocoa. Mix until smooth.
Make the rolls
When the dough has doubled in size, knead a few times in the bowl, just enough to knock out the air.
Lift the dough out onto a lightly floured surface and gently roll out into a 35x25cm (14 inches x 10 inches) rectangle - just a bit bigger than A4 paper.
Spread with the cinnamon chocolate butter.
Starting along one of the long edges, carefully roll the dough up into a sausage shape. Pinch all along the seam to seal.
Slice into 12 pieces. I find it easiest to cut into four, then cut each of those pieces into three.
Spritz the tray with oil and place the rolls into it in a 3x4 pattern.
Cover the tray and place in a warm place for 30 minutes.
Once risen, preheat the oven to 200C (180C fan / 390F). Brush the buns with 1 tbsp of milk.
Place the tray in the oven and bake for 18-20 mins until golden brown. Remove the rolls from the oven and place the tray on a wire rack.
Make the chocolate glaze
Put the icing sugar, milk and cocoa in a small bowl. Whisk together until you have a smooth, thick, glossy icing.
When the rolls have cooled for 10 minutes, pour the glaze all over them.
Leave to cool for 10 more minutes before serving. These gorgeous chocolate cinnamon buns are best served warm and gooey.
Video
Notes
These buns will keep quite well for up to 3 days if stored in an airtight container and placed in a cool, dry place out of direct sunlight.