In the bowl of a stand mixer fitted with the paddle attachment, or a large bowl, stir together 300 grams flour, cinnamon, and salt. Pour in the activated yeast and the milk. Add in the egg and mix on low until the dough begins to come together. Add in the softened butter, a little at a time, waiting until the butter is fully mixed into the dough before adding more to the bowl. Once the dough has come together (it will be very soft and sticky), sprinkle with the remaining 10 grams of flour and allow to rest for about two minutes.