Add the warmed milk and 1/4 cup of the granulated sugar to a stand mixer bowl, stir to combine.
Add the yeast atop and lightly stir to mix in the yeast. Allow the yeast to activate and get foamy, about 5 minutes or so.
Once the yeast has activated, add 1/4 cup of flour and mix to combine. It will still be lumpy.
Add the remaining granulated sugar, the egg, salt, and baking powder. Using the bread hook of the mixer, turn it onto “stir" and combine the ingredients.
Turn the mixer to low or 2 and add the remaining flour. When the flour has mixed in thoroughly, up the mixer speed to 3 or 4 and add the butter, slowly one tablespoon each drop. It will stick to the sides and smear all over, but that’s ok, eventually it will mix in. The dough will be sticky. If need be, if the dough is too gooey, you may add up to 1/4 more flour to hold things together.
Once the butter has combined, beat the dough on 3 or 4 (medium) for 4 minutes. It will be quite soft and still sticky.
Grease a large bowl lightly, add the dough and cover tightly with plastic wrap. Set the dough in a warm place to rise to double its size or about 1 1/2 to 2 hours.
When the dough has risen, melt the first 4 filling ingredients together in a microwave safe bowl, 30 seconds at a time and stirring in between until smooth, probably only 30 seconds to one minute. Once everything is smooth, add the powdered sugar and combine until smooth again.
Flour your work surface and roll out the dough with a floured rolling pin into a rectangle about 13x19.
With an offset spatula, cover the entire surface of the dough with the chocolate mixture, spreading evenly.
Roll up the dough on the 19” edge carefully and slice the dough into 1 1/2” pieces. Place the dough into a lightly greased 9x13 or slightly smaller pan about an inch apart. Cover with plastic and allow to rise again for a half hour.
While the dough is rising its second time, preheat the oven to 350° F or 176° C.
Remove the plastic wrap and bake the rolls for approximately 30 minutes, until lightly golden. Let the rolls cool in the pan.
Once the rolls have cooled, blend the cream cheese and butter in the mixer until they are smooth and fluffy. Add the powdered sugar and vanilla, beat to combine then slowly add the milk 1 tablespoon or less at a time until the frosting is the consistency you desire.
Spread the frosting over the buns and enjoy while they are still warm. Cover with plastic wrap to store once the rolls have completely cooled.