First, make the tang zhong. Place the flour and water into a small saucepan and place over a medium heat, whisking, until the mixture is cooked into a claggy gel. Set aside to cool.
To make the buns, place the four, cocoa, salt, sugar and yeast into the bowl of a stand mixer.
Whisk together the tang zhong and milk. Pour that into the dry ingredients, and crack in the eggs. Using the dough hook, work the mixture on a low speed, just until it begins to come together in a dough.
Slowly add the butter, about a teaspoon at a time, working well in between each, and mix until all the butter has been incorporated. You should have a sticky, dark brown dough. Scrape down the bowl, cover with plastic, and set aside in a warm place until doubled in size (anything from 1-2.5 hours).
When the dough has risen, add in the chocolate, cranberries, ginger and hazelnuts, and mix until everything is incorporated. Turn the dough out onto a floured surface and divide into 10 even pieces. Roll each piece into a ball and place on a paper-lined baking sheet. Cover lightly with plastic and set aside to rise again for about 40 minutes.
Preheat the oven to 160C/325F. When the buns are risen, make the crosses on top. Mix the flour with about 3 tbsp water to form a thick paste. Transfer to a piping bag with a small round tip, and pipe crosses across the top of the buns.
Bake the buns for 20 minutes, or until they are risen, are a dark matte brown, feel springy and spongey to the touch, and sound hollow when tapped.
Mix the sugar with a splash of boiling water, just to dissolve the sugar and form a syrup. Brush the syrup over the hot buns and then set aside to cool. Serve warm.
Recipe by The Sugar Hit at http://www.thesugarhit.com/2016/03/chocolate-hot-cross-buns-with-ginger-cranberry.html