In the bowl of your stand mixer, with dough hook attached, add flour, salt, yeast, cocoa powder, sugar, egg and additional yolk, and milk. Mix on low until dough comes together.
Add half of softened butter in and mix until incorporated into the dough and then add remaining butter.
Mix dough on low-medium until dough is smooth and soft, and no longer sticking to the sides of the bowl.
Remove dough from bowl, and shape into a ball. Lightly grease bowl, and place dough inside, covering. Place in a warm spot to rise for 90-120 minutes or until dough has doubled in size.
Line a 9 inch square pan, preferably metal, with parchment. Set aside.
Set up a double boiler and bring the water to a simmer.
Punch down the dough and place on your work space. Roll out the dough into a 10x15 inch rectangle. Cover your dough while you make the filling.
Add your butter, chocolate bar and salt to the double boiler. Once the chocolate has melted, remove from heat and stir in your cocoa powder and cinnamon.
The filling should cool pretty quickly, and once it's no longer hot (it's fine if it's warm) spread your chocolate filling over the surface. Leave a ½ inch border on the short sides and all the way to the edge on the long sides.
Roll your dough up on the short side into a log, pinching the seams to seal.
Using either a serrated knife or thread/unflavored dental floss, cut your dough into 9 equal pieces.
Place each roll into your prepared pan. Cover your pan and allow to rise for another 30-45 minutes. The rolls will be puffy and larger.
Preheat your oven to 350°F while your rolls proof.
When ready, place your rolls into the oven on the center rack and bake for about 22 minutes. The rolls will be lightly golden on the edges and you should be able to see the filling set and they should smell strongly of chocolate.
While your chocolate sweet rolls cool, prepare your frosting. In a small bowl add your cream cheese and powdered sugar and use a hand mixer to mix together until smooth.
Add your salt and cocoa powder and blend for another 30 seconds to a minute.
Add your milk and mix for another minute or so until the frosting is smooth and creamy.
Spread your frosting onto the rolls while warm but not hot. Sweet rolls are best served warm and same day, but can be stored in an airtight container for 2-3 days. Enjoy!
