1. For the dough: add the milk, syrup and butter to a small saucepan and warm through. Once the butter is melted check that the mixture is lukewarm (you may need to leave it for 5-10 minutes to cool).
2. Add the flour, cocoa powder, yeast and salt to a large mixing bowl and stir to combine.
3. Using a freestanding mixer with the dough hook attached, gradually pour in the milky mix until combine. Knead for 5 minutes over a low speed, or until springy and doughy (it may appear sticky and won’t ball up). If kneading by hand, knead for 8-10 minutes, until soft and supple.
4. Place into a greased bowl, cover and leave somewhere warm for 1 hour, or until doubled in size.
5. Prepare the filling: stir together the sugar and cinnamon.
6. Lightly flour a work surface. Punch the risen dough down and tip onto the surface. Roll out the dough to about a 14 inch square. Brush over ⅔ of the melted butter, sprinkle over the cinnamon sugar, chocolate and hazelnuts, leaving a small gap around the edge.
7. Use one side to carefully and fairly tightly roll up into a log. Trim off the edges and using a knife or piece of cotton, divide into 9-12 rolls.
8. Butter the base of an 8-inch oven-proof dish (perfect for 9 rolls) and nestle in the rolls so they are just touching. Cover and leave somewhere warm for 30-45 minutes till risen and almost doubled again.
9. Preheat the oven to 350*F. Uncover the risen buns, brush with the remaining melted butter and bake for 30-35 minutes, until risen, fluffy and starting to darken on top. Allow the buns to cool for 30 minutes or to cool fully.
10. Prepare the glaze: whisk together the ingredients till smooth.
11. Spread over the glaze, topping with more chocolate and hazelnuts and enjoy.
12. Once fully cool, cover the buns tightly and keep for 1-2 days in the fridge although best enjoyed at room temperature.