1. **Make the Tangzhong:** In a small saucepan, whisk together 25g bread flour and 125ml milk until smooth. Cook over medium-low heat, stirring constantly with a whisk or rubber spatula, until the mixture thickens to a paste-like consistency (about 65°C or 149°F). It should leave trails when stirred. Remove from heat, transfer to a small bowl, cover directly with plastic wrap to prevent a skin from forming, and let cool completely to room temperature (this can take 1-2 hours or be done the night before and refrigerated).

2. **Activate the Yeast:** In a large mixing bowl (or stand mixer bowl), combine 100ml warm milk and instant yeast. Let sit for 5-10 minutes until foamy, indicating the yeast is active.

3. **Combine Dry Ingredients:** Add the remaining 300g bread flour, sugar, and salt to the yeast mixture. Add the cooled Tangzhong paste.

4. **Knead the Dough:** Mix on low speed (with a dough hook if using a stand mixer) until a shaggy dough forms. Increase speed to medium and knead for about 10 minutes until the dough starts to come together and is somewhat smooth. It will still be a bit sticky.

5. **Add Butter:** Add the softened butter, one piece at a time, incorporating each piece before adding the next. Continue kneading for another 10-15 minutes until the dough is very smooth, elastic, and passes the windowpane test (you should be able to stretch a small piece thin enough to see light through it without tearing).

6. **First Rise (Bulk Fermentation):** Form the dough into a ball and place it in a lightly oiled bowl. Cover with plastic wrap or a damp towel and let rise in a warm place for 1.5-2 hours, or until doubled in size.

7. **Shape the Loaf/Rolls:** Gently punch down the risen dough to release air. Transfer to a lightly floured surface. For a loaf, divide the dough into 3 equal pieces. Roll each piece into an oval, then fold the sides to the center and roll up tightly into a cylinder. Place the cylinders seam-side down in a greased 9x5 inch loaf pan. For rolls, divide the dough into 12 equal pieces, form into smooth balls, and place on a baking sheet lined with parchment paper, leaving space between them.

8. **Second Rise (Proofing):** Cover the loaf pan or baking sheet loosely with plastic wrap or a damp towel and let rise again in a warm place for 45-60 minutes, or until nearly doubled in size and puffy.

9. **Preheat and Bake:** Preheat your oven to 180°C (350°F). Bake the loaf for 25-30 minutes, or the rolls for 18-22 minutes, until golden brown on top and cooked through. If the top browns too quickly, tent loosely with foil. An internal temperature of 90-93°C (195-200°F) indicates it's done.

10. **Cool:** Remove from the oven and let cool in the pan for 10 minutes before transferring to a wire rack to cool completely before slicing or serving.