Add in 4 cups of flour, and mix with the dough hook for 5 minutes. If the dough is still sticky and has not removed itself from the sides of the bowl, add in the remaining 1/2 cup of flour, 1/4 cup at a time, and mix the dough until it is tacky, not sticky.
Shape dough into a ball and place the dough in an oiled bowl. Cover with a damp cloth and let it double in size in a warm place (about 30-60 minutes).
With a standing mixer or hand mixer, add the powdered sugar into the brown sugar mixture, and mix until the frosting is smooth (frosting will feel thin).
Spread the frosting over the tops of the warm rolls immediately, or let the frosting sit and thicken up, then spread it over the rolls.
*Pumpkin butter: Using 2/3 cup pumpkin butter will make the rolls a bit more gooey. You can use homemade or store-bought pumpkin butter. My favorite is Williams-Sonoma Pumpkin Pecan Butter.
**Overnight: If you are making these the night before, after you cover the rolls with plastic wrap for their second rise, store them in the fridge for up to 18 hours. Remove the rolls from the fridge 1 hour before baking (you will probably need 30-60 minutes for the rolls to reach room temperature and double in size). Once they have risen, bake as directed in the recipe.