In a large mixing bowl add the warm milk, instant yeast and sugar. Stir and let it sit for 10 minutes or until frothy.
Add the egg, flour, salt, vanilla, water and stir together until a shaggy dough. Pour in the melted butter and stir into the dough.
Once it gets tough to mix, remove the spatula and use your hands to knead the dough together until to form a ball around 1 - 2 minutes.
Place the dough in the same mixing bowl and cover with cling wrap. Let this rest and rise for 45 minutes to 1 hours or until doubled in volume.
In the mean time let us make the chocolate filling. In a mixing bowl add the butter, brown sugar, cocoa powder, cinnamon powder and salt - whisk until it is combined and smooth.
Once the dough is doubled in volume remove from the bowl onto a clean kitchen surface and sprinkle a little flour with baking powder. Roll out the dough to 9x13 inches.
Spoon over the chocolate butter spread evenly and cut the dough with a pizza cutter into 6 strips. Sprinkle over the chopped chocolate and mini marshmallows.
Roll up each piece into scroll and place in a 9x6 baking tray. Repeat the process until all the pieces are in the baking tray. Cover with cling wrap and allow it to rise for 15-20 minutes.
In the mean time preheat the oven to 180℃. Once risen, bake the rolls in the oven for 25 minutes. While they are baking make the fudge frosting by mixing icing sugar, cocoa powder, hot water and salt in a bowl until thick and smooth. Add 1 tbsp milk into the frosting and stir again.
As the buns are out of the oven spread the frosting on top of each of them while warm/hot. Top with jumbo marshmallows and torch until toasted. You can do this step in the oven under broiler as well for a couple of minutes. Top with chocolate chips while still warm.
Serve them warm/hot with a glass of milk for the perfect treat.