Place the flour, tangzhong, cardamom, sugar and salt in a free standing mixer. Heat the milk in a saucepan to 38C, remove from the heat and add the fresh yeast and stir. If you’re using fast action pour it over the flour. Pour the milk mixture over the flour and turn the mixer on medium-low. Now add the egg and blend for a minute or so. Once the egg is incorporated add the butter and continue to mix. Once it has blended with the dough increase the pace to medium-high and work the dough for another 6-8 minutes or until it feels smooth, silky and shiny. Flour your work surface lightly and place the dough on top, shape into a round, pop back into a clean bowl and cover with a damp tea towel and prove for 20-30 minutes. (Cover with plastic wrap if you're proving in the fridge overnight).
Mix together the butter, sugar, cocoa to make a smooth paste.
Shaping the dough: On a lightly floured surface, roll the dough out into 80x40cm. Spread the chocolate butter mixture on approximately half of the surface. Fold the dough in half, then roll again gently to make an approximate rectangle measuring 45x30cm.
Cut the dough into roughly 2cm wide strips, I find a pizza wheel good for this job. Twist each strip several times, slightly stretching it as you do so. Cut another strip in half and coil it round the bun, tucking the ends underneath. Continue with the rest of the strips.
Arrange the buns on a baking sheet lined with parchment paper (if they’re too crowded, use 2 sheets), keeping as much space between them as possible. Cover and let prove for 30–45 minutes or until doubled in size.
Meanwhile, set the oven shelf to the middle position and preheat to 200C Fan.
Brush the buns with an egg wash, sprinkle with sugar nibs, and bake for 10-12 minutes or until golden brown. Allow buns to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
The buns are best the same day they are made, but can be frozen for up to 2 months and reheated in the oven before serving.