Generously butter a 1-inch (2.5 cm) cast-iron skillet or cake pan.
In a large bowl, whisk together the warm milk, melted butter, and granulated sugar. The mixture should be just warm, registering between 100-110˚F (40˚C). If hotter, allow to cool slightly before proceeding.
Sprinkle the yeast evenly over the warm mixture and let sit for 1 minute. Add 4 cups of the flour to the milk mixture and mix with a wooden spoon until just combined. Cover the bowl with a towel or plastic wrap and set in a warm place to rise for 1 hour.
After 1 hour, the dough should have nearly doubled in size. Remove the towel and add an additional ¾ cup (95 grams) of flour, the baking powder, and salt. Stir well, then turn out onto a well-floured surface.
Knead the dough lightly, adding additional flour as necessary, until the dough just loses its stickiness and does not stick to the surface.
Roll the dough out into a large rectangle, about ½ inch (1.5 cm) thick. Fix corners to make sure they are sharp and even.
Make the filling: In a small bowl, combine the softened butter, light brown sugar, and cinnamon.
Spread the filling mixture evenly over the rolled-out dough, spreading right to the edges.
Using a pizza cutter, make 3 horizontal cuts to divide the dough into 4 long, evenly-sized strips. Starting from the top, roll the first strip up from right to left. Take the first roll and place it on top of the next strip, starting again on the right side and rolling up right to left, building on the first. Continue with the remaining strips until you have a giant cinnamon roll.
Place the giant cinnamon roll in the prepared skillet or cake pan and cover with plastic wrap. Place in a warm spot and leave to rise for 30 minutes. The cinnamon roll should expand to the edges of the pan during this time.
Preheat the oven to 325˚F (160˚C).
Uncover the cinnamon roll and bake for 45 minutes. Cover the roll with foil to prevent the outside from burning, and bake for an additional 35 minutes.
While the cinnamon roll is baking, prepare the frosting: In a medium bowl, whisk together the cream cheese, butter, milk, vanilla, and powdered sugar until smooth.
Remove the cinnamon roll from the oven and let cool in the pan for at least 20 minutes. Once cool, remove from the pan and drizzle the frosting over the roll before serving.