Use a digital scale to measure out the ingredients.

In a 2-quart saucepan, combine 55 g of the milk and the mochiko. Whisk to combine and cook over medium heat, stirring constantly, until the mixture thickens to a paste, about 2-3 minutes. Transfer to a small bowl and let cool to room temperature.

In a medium bowl, whisk together the remaining 80 g of milk, the egg, and the nonfat dry milk powder.

In the bowl of a stand mixer fitted with the dough hook, combine the bread flour, sugar, and salt. Add the milk-egg mixture and the cooled tangzhong. Mix on low speed until a shaggy dough forms, about 2 minutes.

Increase the speed to medium and knead for 5 minutes. Add the softened butter and continue kneading until the dough is smooth, elastic, and passes the windowpane test, about 10 minutes more.

Lightly grease a large bowl. Transfer the dough to the bowl, cover, and let rise at room temperature until doubled in size, about 1 hour.

Punch down the dough to release any air bubbles. On a lightly floured surface, use a bench scraper to divide the dough into 3 equal pieces. Working with one piece at a time (keep the rest covered), use a rolling pin to roll the dough into a 9-inch square. Fold the dough into thirds like a letter, then fold in half to create a small package. Place seam-side down in the prepared Pullman loaf pan. Repeat with the remaining two pieces of dough.

Cover the pan and let the dough rise at room temperature until it reaches the top of the pan, about 1 hour.

Preheat the oven to 350°F. Bake the bread for 30-35 minutes, until the internal temperature reaches 205-210°F. Remove from the oven and let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.