Preheat oven to 350 degrees. Line rimmed baking sheet with silicone baking mat or parchment paper, spray lightly with nonstick cooking spray and set aside.
In a large bowl (or stand mixer), combine 4 cups of flour, 2 packets of rapid rise yeast, and 1 tsp salt.
In a microwave safe bowl, combine 1 cup milk, 1/4 cup granulated sugar, and 1/3 cup butter. Microwave for 30 seconds or until butter is melted. Mix together an let cool.
Once cooled (warm, not hot!), slowly pour the warm milk mixture into the flour mixture and mix together by hand or with a stand mixer on low. Add your egg and continue to mix until a sticky dough ball forms.
Add in 2 tablespoons of flour at a time until it starts pulling away from the bowl. You still want it to be a little sticky otherwise you'll end up with dense cinnamon rolls. Let the dough rest for 5 minutes.
Sprinkle counter with flour and roll dough out to be about 1/4 thick and 12x16 inches.
Using a spatula, spread 1/3 cup softened butter over dough, leaving a 1 inch strip untouched on the longer sides of dough (this will help you seal off the roll and keep it tight).
Sprinkle the brown sugar/cinnamon filling evenly over the butter.
Starting with the long end, roll the dough tightly towards the untouched strip.
Using dental floss, cut off the uneven ends (slide the floss under the roll, take both ends of the floss, cross them over the top of the roll, and pull on the ends to slice). Then continue to slice your rolls into 1 1/2 inch rounds and place on on your prepared baking sheet.
Cover the rolls with a dish towel and let rise on top of the oven (or other warm place) for 20-25 minutes until puffy.
Bake for 20 minutes or until they are light golden brown.