Pour the warm milk in the bowl of a stand mixer and sprinkle the yeast overtop. Let the mixture sit for 5-10 minutes until foamy. Add the eggs, butter, salt and sugar.
Add in 4 cups of flour and mix using the beater blade just until the ingredients are barely combined. Allow the mixture to rest for 5 minutes so the flour has time to soak up the liquids.
Scrape the dough off the beater blade and remove it. Attach the dough hook.
Beat the dough on medium speed, adding in up to 1/2 cup more flour if needed to form a dough. Knead for 5-7 minutes or until the dough is elastic and smooth. **The dough should be tacky and will still be sticking to the sides of the bowl.
Spray a large bowl with cooking spray.
Use a rubber spatula to remove the dough from the mixer bowl and place it in the greased large bowl.
Cover the bowl with a towel or wax paper.
Set the bowl in a warm place and allow the dough to rise until double. (about 1 - 1 ½ hours, this will vary depending on how warm your kitchen is. The colder the kitchen the longer the rise. You can speed this up by putting your bowl in an oven. To proof in your oven: Preheat your oven at it’s lowest temperature for 1-2 minutes, then turn it off. Place your bowl of covered dough in after it’s off.
While the dough is rising, prepare the cinnamon filling. In a medium bowl, combine the soft butter, brown sugar and cinnamon, mixing until well combined. Set aside.