In a large bowl or the bowl of a stand mixer, whisk together the sugar and yeast. Heat the milk and water together either in the microwave or on the stovetop until it's warm to the touch (about 110F). Pour the milk mixture over the yeast and sugar and whisk it together. Then loosely cover it and let it sit for 5 minutes, until it's frothy. Then use either a rubber spatula or a dough hook if you're using a stand mixer and beat in the butter until it's slightly broken up.
Next add 2 1/2 cups of the bread flour, the salt and the cinnamon and mix until combined (med-low speed). Then add additional bread flour (about 1/2 cup, maybe a bit more) until you get a soft dough that no longer sticks to the sides of the bowl. Then you either want to knead with floured hands or with the mixer on medium speed for 2 minutes, until the dough is smooth and still slightly soft.
Shape your dough into a ball and place it into a large, greased bowl. Turn the ball to coat all sides, then cover it tightly with plastic wrap or foil and let it rise someplace warm for 1-2 hours, or until doubled in size. Towards the end of rise time, mix together the remaining sugar and cinnamon for your bread filling in a small bowl and set it aside. Also grease a 9x5" loaf pan with either more butter or with non-stick spray and set it aside.
Punch down the dough to release the air, then place it onto a floured surface. Use a floured rolling pin to roll it out into a rectangle (9x18"). Sprinkle the cinnamon sugar mix over the dough, leaving a border around the sides. Then roll it up very tightly into a 9" log. Pinch the ends together to seal or tuck them slightly under. Place into the prepared loaf pan and cover loosely. Allow it to do a 2nd rise someplace warm until the dough rise to the top of the pan, about 1 hour.
Adjust your oven rack to the lower third position and preheat to 350F. Gently brush the melted butter over the top of the dough. Bake until the loaf is golden brown and when it's gently tapped, the top of the loaf sounds hollow, about 35-45 minutes. If you notice the bread browning too quickly while it bakes, then loosely tent foil over the top.
Once it's done, place the pan on a wire rack to cool for 10 or so minutes. Then remove the loaf from the pan and let it cool completely on the wire rack before slicing and serving. Keep leftovers covered for 4-5 days or store in the fridge for up to 1 week.
