In a small saucepan on low-medium heat, combine the starter ingredients. Whisk continuously for about 5 minutes or until the starter thickens to the consistency of mashed potatoes. Remove from heat and let cool to room temperature.
Activate the yeast and heat the milk to lukewarm temperature and sprinkle the yeast over the surface of the milk. Do not mix and let it sit undisturbed for about 5 minutes. If the yeast is active, bubbles should appear on the surface. Set aside.
In a large bowl, combine bread flour, sugar, yeast, dry milk powder, and salt. Then add the milk with activated yeast, starter, and beaten egg. Using the dough hook attachment, beat on low speed for about 5 minutes. Add in butter and beat for another 5 minutes. Increase the speed for the final 5 minutes, and continue kneading until the dough passes the windowpane test. Transfer to bowl and cover with plastic wrap or towel. Let it rest for 1 hour or until dough has doubled in size.
Turn dough onto lightly floured surface and punch the dough down to release air bubbles. Divide into 4 equal pieces and roll out each to a rectangular shape about 8"x4" (20cm x 10cm) long. Roll up from the shorter side and place in a lightly greased 9"x4" (23cm x 10cm) bread pan. Repeat until all dough is in the pan. Cover and let it rest for 45 minutes.
Preheat oven to 350°F/180°C. After the second rest, brush the top of the dough with egg wash or melted butter. Bake for 35-40 minutes or until the top is golden brown. If the top is browning too quickly but the inside is not done yet, loosely cover the top with aluminum foil to prevent it from burning.
Remove from oven and let cool for 5 minutes in the bread pan before transferring to a cooling rack. Let cool for at least 10 additional minutes before slicing.