In a large mixing bowl, combine 2 cups of flour, sugar, yeast, and salt.
Stir until blended.
In a separate microwave-safe bowl, combine water and butter.
Microwave in 15-second increments until the mixture is very warm but not hot to the touch (between 120°F and 130°F).
Add this warm liquid to the flour mixture.
Beat the mixture for about 2 minutes at medium speed using an electric mixer.
Scrape the sides of the bowl as needed.
Stir in enough remaining flour to make the dough easy to handle.
Knead on a floured surface until the dough is smooth and elastic
Shape the dough into a ball and let it rest for about 10 minutes.
Roll the dough into a 15 x 10-inch rectangle using a rolling pin.
Spread 3 tablespoons of soft butter over the dough, leaving at least a 1/2-inch border on the long sides.
Sprinkle the cinnamon sugar mixture evenly over the butter.
Starting at the long end of the rectangle, roll up the dough tightly.
Pinch the seams to seal.
Cut the rolled dough into 12 equal pieces.
Place the rolls in a greased baking pan and let them rise in a warm place until they have doubled in size, which takes about 1 hour.
Preheat your oven to 350°F (175°C) and bake the rolls for 25 to 30 minutes, or until they are golden brown.
Once done, allow them to cool on a wire rack for at least 20 minutes.
To make the frosting, combine all the frosting ingredients in a large bowl (begin with 2 tablespoons of milk and add more if needed) and beat until creamy.
Spread the frosting over the cooled cinnamon rolls.