In a saucepan, whisk together the milk, espresso and melted butter. Heat the mixture to just warm, about 37 - 39 degrees or similar to a warm bath. Gently mix the yeast into the milk and cover with a towel and leave to activate. A healthy activated yeast will start to pop to the top and bubble - the top of the mixture should be foamy and frothy. This can take up to 10 minutes. (If your milk mixture is too hot you will kill the yeast and it will not activate!)
Transfer to a bowl and then add 600g of the flour, salt and baking powder. Mix with a wooden spoon until just combined. Cover the bowl with a towel or plastic wrap. Put the covered dough into a warm place for at least an 1 hour. It should double in size.
Remove the cover and add the remaining flour. Stir well, then turn out onto a well-floured surface. Knead the dough lightly, adding additional flour as necessary, just until the dough loses its stickiness and does not stick to the surface. Roll the dough out into a large rectangle. Mix together the ingredients for the filling and spread evenly over the dough. Cover with the chocolate chips and a dusting of cocoa powder.
Cut the dough into 6 pieces for giant rolls, or 9 for smaller rolls. Place the rolls in a lined and greased tin then cover and leave to rise again in the oven or warm place for a couple of hours. Preheat the oven to 180. Remove plastic wrap. Bake the rolls at 180˚C for 25-30 minutes, until golden brown. Whilst the rolls are baking make the glaze. Dissolve the coffee in the hot water. Mix together the cocoa powder and sugar then slowly add in the coffee and milk. Mix until smooth.
Cover the rolls whilst still warm and then leave to set for about 30 minutes before serving.