In the bowl of a stand mixer, combine the milk, instant yeast, sugar, eggs, butter, 3 ½ cups flour, cocoa powder and salt. With a dough attachment, mix the ingredients until the flour is incorporated, about 4-5 minutes. If dough is too sticky, add flour 1 tablespoon at a time but it's better to be on the sticky side. Cover the dough with plastic wrap and let rest at room temperature for 1 hour or until it has doubled in size.
In a small bowl, mix together the light brown sugar, cinnamon and salt for the filling. Set aside.
Lightly dust your work surface with some flour. Remove dough from mixing bowl and punch down. Roll the dough to about ¼" thick and a rectangle about 14x10 inches. It doesn't have to be perfect. I use a 9x13 baking dish as reference.
Spread the softened butter evenly over the dough. Sprinkle the cinnamon mixture over the butter and lightly push into the butter. Sprinkle chocolate chips over top.
Starting with the long edge close to you, roll the dough into a log, trying to keep tight throughout. With a sharp knife, cut 12 rolls about 1" thick. Place the rolls in a greased 9x13 baking dish. Cover with plastic wrap and transfer to fridge so it can rise overnight. (You can let rise for 30 minutes at room temperature in a pinch)
Preheat oven to 350°F. Bake the rolls for 25-30 minutes or until golden brown on top and the middles are done.
While the rolls are baking, make the frosting. In a stand mixer, beat together the butter, cream cheese, powdered sugar, cocoa powder, vanilla extract and salt until smooth. If the frosting is too thick, just add 1 tablespoon of milk at a time until it reaches your desired consistency.
Spread the frosting over the warmed rolls and serve immediately.