In a food processor, whisk 120 ml milk with 1 tablespoon sugar and yeast and let sit for about 5 minutes until foam forms on the surface. Add the remaining milk, sugar, salt and eggs and mix on low speed for 1 minute. Use the dough hook.
Sprinkle in 730 g flour and knead the mixture, first on low speed, then on medium speed, for 3 minutes until a fairly smooth dough forms. Reduce the speed to medium-low and knead in the butter and remaining flour.
Continue kneading the dough with your hands on a floured work surface for about 2 minutes, until it is smooth, pliable, and no longer sticky.
Shape the dough into a ball, place in a bowl thinly greased with oil, cover the bowl, and let the dough rise in a warm, draft-free place until doubled in volume, about 1½ hours.
For the filling, mix sugar and cinnamon. Press the risen dough together firmly in the bowl, then knead two or three times on a lightly floured work surface.
Roll out the dough into a 60 x 30 cm rectangle. Brush the entire sheet of dough to the edges with 6 tablespoons of softened butter and sprinkle evenly with the cinnamon sugar.
From the long side facing you, roll up the dough sheet tightly to the end and press the seam firmly along the entire length. Cut the dough roll into twelve pieces, each 5 cm wide.
Grease the bottom and sides of the cast iron pan or baking dish gr