Add the milk, granulated sugar and yeast to a mixing bowl - give it a stir and let the mixture sit for 10 -15 minutes until the yeast blooms.
Add the dough hook attachment to your stand mixer. (If you don't have a stand mixer then use a mixing bowl and a spatula to mix the ingredients).
To the yeast mixture, add the butter, eggs, vanilla essence and castor sugar and mix.
Then add the flour, salt, cinnamon, cocoa powder and mix until the ingredients are mostly incorporated and then add the buttermilk.
Lastly add the chocolate chips and mix for 2 minutes - kneading in the bowl.
Transfer the dough to a floured surface and continue to knead by hand for 5 minutes.
Place the dough in a lightly oil greased bowl, cover with clingwrap and a kitchen towel and let it rise in a warm area for 1½ hours.
Grease and line a 33x22cm baking pan or baking sheet.
Shape the dough into 12 even sized balls - use a kitchen scale to weight each ball (weighing about 90-95g each). Place on the baking pan/sheet, leaving enough space in between.
Cover with clingwrap and a kitchen towel and let it rise for a second time for 1 hour.
Preheat the oven to 180°C.
Crack the egg and mix with water to prepare the egg wash and brush each bun with it.
Mix the flour and water for the cross toping. Place in a piping bag/ziploc bag and snip a small piece off. Pipe a line through the centre of each bun and then pipe another line in the opposite direction to form the cross.
Bake for 25 minutes - remove from the oven and let it cool for 5 minutes.
For the glaze - add the apricot jam and water to a small bowl and microwave for 20 seconds.
Brush the glaze over the warm chocolate buns. Serve and enjoy!