Make the tangzhong. In a small saucepan, whisk 25 g flour with 120 ml milk until smooth. Set over medium-low heat and cook, whisking, until thick like pudding and the whisk leaves lines, 2–3 minutes. It should reach about 65°C, but you don’t need a thermometer if it thickens nicely. Scrape into a bowl and let cool to lukewarm. A few gentle breaths. No rush.

Mix the dough. In the bowl of a stand mixer (or a large bowl), combine 320 g flour, sugar, instant yeast, and salt. Add the egg, warm milk, and the cooled tangzhong. Mix on low until a rough dough forms, 1–2 minutes.

Knead and add butter. With the mixer on medium-low, knead 5 minutes. Add the soft butter in small pieces, letting each piece disappear before the next. Continue kneading 6–8 minutes more, until the dough is smooth, elastic, and slightly tacky but clears the bowl. If kneading by hand, it’ll feel sticky at first. Keep going; it comes together. You’re aiming for a windowpane that stretches thin without tearing.

First rise. Shape the dough into a ball and place in a lightly oiled bowl. Cover and let rise in a warm spot until puffy and about doubled, 60–90 minutes. If your kitchen is cool, give it a little extra time. No stress.

Shape. Gently deflate the dough onto a lightly floured surface. Divide into 3 or 4 equal pieces. For each piece: pat into a rectangle, fold the short edges toward the center like a letter, then roll up tightly into a short log. Place the logs seam-side down in the greased loaf pan, side by side.

Second rise. Cover and let rise until the dough domes about 2–3 cm above the pan rim and springs back slowly when touched, 45–75 minutes, depending on room temperature.

Preheat and bake. Heat the oven to 175°C/350°F. Lightly brush the top with milk or egg wash. Bake 28–35 minutes until deep golden and the center reaches about 88–93°C/190–200°F. If the top browns early, tent loosely with foil. The kitchen will smell like a bakery. That’s your timer too.

Finish and cool. Optional: brush the hot loaf with a little soft butter for a gentle sheen. Cool in the pan 10 minutes, then move to a rack. Let it cool at least 45 minutes before slicing for the fluffiest crumb. If you can wait. I rarely do.