• Sift the bread flour and milk powder into the mixing bowl. Add the sugar, instant yeast, half of the beaten egg, and water (Image 1). Attach the dough hook and begin mixing (Image 2). Once the ingredients come together into a rough dough, add the unsalted butter and salt (Image 3). Continue kneading until the dough becomes smooth and elastic, about 17 minutes in my mixer. Check the dough with the windowpane test—it should stretch into a thin, translucent membrane without tearing easily (Image 4).
• Take one portion and flatten it gently with your hand. Roll it out with a rolling pin, flip it over, and roll again (Image 8). Place one piece of cold salted butter in the center (Image 9). Bring the edges of the dough toward the center and pinch firmly to seal the butter inside (Image 10). Repeat with the remaining dough.
• Shape the dough into a smooth ball and place it in a bowl (Image 5). Cover with plastic wrap to prevent the surface from drying out, then let it rise for about 1 hour, or until doubled in size. Gently press the dough to release the excess air (Image 6). Divide it into 6 equal portions, shape each portion into a ball, and cover with plastic wrap (Image 7). Let the dough rest for 10 minutes.
• Arrange the shaped buns on a lined baking tray and cover loosely with plastic wrap (Image 11). Let them rise again for about 40 minutes, or until noticeably puffy and close to doubled in size (Image 12). Meanwhile, prepare the coffee topping (see the coffee topping instructions below). Pipe the topping in a spiral, starting from the center and working outward (Images 13, 14).
• Bake in a preheated 356°F (180°C) oven for 16–20 minutes, or until the tops are deeply golden and crisp.
• Once baked, the coffee topping should form a crisp crust over the surface of the buns (Image 15). Transfer the buns to a cooling rack and let them cool slightly.
• For the best texture, enjoy the coffee buns while still warm. When you tear one open, the bread should be soft and fluffy, with the salted butter melted inside (Image 16).

Coffee Topping

• Dissolve the instant coffee powder in the hot water in a mixing bowl (Image A). Add the unsalted butter and mix until well combined (Image B). Add the reserved half of the beaten egg and mix again until smooth (Image C).
• Add the powdered sugar and all-purpose flour (Image D), then mix until you have a smooth, creamy coffee topping (Image E). Transfer the mixture to a piping bag (Image F) and set aside until ready to use.