For the rolls

1. In a medium bowl, whisk together flour, yeast, and salt.  Set aside.
2. In the bowl of a stand mixer fitted with the paddle attachment, mix the melted butter, sugar, sour cream, and egg.  With the mixer on low speed, add half of the flour mixture followed by the milk, and mix until combined.  Switch to the dough hook attachment and add the remaining flour mixture.  Beat on medium speed for 5-7 minutes, or until dough is smooth and elastic.
3. Lightly grease a large bowl with vegetable oil or cooking spray.  Place the dough in the bowl.  Rotate the dough so that it is greased on all sides.  Loosely cover and allow to rise in a warm place (75°F/24°C) until doubled in size, about 1 hour.
4. Grease a 13x9-inch baking pan with butter or cooking spray.
5. Turn out dough onto a lightly floured surface and lightly punch down to release some of the gases.  Roll dough into an 18x12-inch rectangle.

For the filling

1. Spread softened butter onto the dough.  In a small bowl, mix the brown sugar and cinnamon and sprinkle on the dough allowing for a ½-inch border along one of the long edges. Brush edge without sugar with beaten egg.
2. Begin with the long edge that has the sugar mixture and roll the dough into a log.  Pinch seam to seal, trim ends, and slice into 12 rolls. Place in prepared pan.  Allow the rolls to rise in a warm place (75°F/24°C) until rolls are puffed, about 30 minutes.
3. Preheat oven to 350°F/176°C.
4. Bake cinnamon rolls 30-35 minutes or until tops are golden brown. Allow the rolls to cool 15 minutes before frosting.

For frosting

1. In a mixer, beat the cream cheese and butter on medium speed until completely smooth and creamy, about 5 minutes. With the mixer on low speed, add powdered sugar, beating until fluffy. Add milk and mix until combined. Spread onto warm rolls.