In a small saucepan, whisk together 27g water, 60g milk, and 20g flour. This is our Tangzhong.
Cook over medium heat, stirring constantly until it thickens into a smooth paste (~65°C or when lines appear in the mixture).
Transfer to a bowl and let cool to room temperature.
In a mixing bowl, combine: Tangzhong, 120g milk, 9g yeast, 320g flour, 35g sugar, 7g salt, 1 whole egg + 1 egg yolk
Mix with dough hook until just combined.
Gradually add softened butter, a few grams at a time, until fully incorporated.
Continue kneading on medium speed with a stand mixer for approximately 20–30 minutes, until the dough is smooth, elastic, and pulls away from the bowl. Perform a windowpane test to check if it’s ready.
Cover and let rise at room temp for 1.5 to 2 hours, or until doubled in size.
Divide the dough and shape it into balls, each weighing between 110 and 120 g.
Place each ball on a parchment paper, on a tray with space between pieces.
Cover and let rise until doubled again (30–60 minutes depending on temp).
Whisk 1 egg with a splash of milk.
Brush the tops of the proofed dough gently.
Top with dried rosemary, toasted sesame seeds, or nigella seeds.
Bake at 175°C (350°F) for 22–24 minutes.