Heat your whole milk in the microwave until it reaches about 120 degrees. Stir in the sugar and vanilla, and then stir in the yeast. Set aside until lightly frothy and bubbled. In a large bowl, stir together the eggs and softened butter. The mixture will be lumpy.
Add the yeast mixture into the egg mixture and stir until combined. Add in the salt, and then add the bread flour 2 cups at a time, mixing between, until you reach 5 cups. Switch to the dough hook attachment (or turn out and knead by hand for 10 minutes) and knead for 5-10 minutes. The dough should bounce back when you poke it.
Cover your bowl and let the dough rise for about 30 minutes, or until it's risen about 1/3 in size. While the dough rises, make the filling.
In a small saucepan, melt the butter and chocolate together until incorporated. Add in the powdered sugar, cocoa powder, salt, espresso powder. The mixture will be thick and soft.
Once the dough has risen, roll it out into a large rectangle about 1/2 inch thick. Spread the filling evenly over the dough all the way to the edges. Sprinkle on the chocolate chips evenly. Roll the dough starting on a long side into a log. Cut the log into 12 even rolls.
Place the rolls evenly into a 13x9 inch cake pan that has been sprayed with baking spray. Cover and let the rolls rise for about 20 minutes until puffed. While this happens, preheat your oven to 375 degrees.
Once the rolls are puffed, uncover and bake for 15-18 minutes, or until lightly golden brown on the tops.
In a medium bowl, microwave the heavy cream until boiling. Add in the chocolate chips, vanilla, and salt, and whisk until smooth. Drizzle over the rolls when they are still warm, and enjoy!