Make the Tangzhong: Whisk milk, water and bread flour in a saucepan until smooth. Cook over medium-low heat, whisking constantly, for 1–2 minutes until thickened. Remove from heat and cool until warm, not hot.

Add lukewarm milk, yeast, sugar and honey to a stand mixer. Stir and let sit for 5 minutes.

Add Tangzhong, bread flour, salt and egg. Mix with the dough hook on low until combined, then knead on medium for 5–7 minutes until smooth and elastic.

Add softened butter one piece at a time, allowing each piece to incorporate before adding the next. Knead another 5–8 minutes until smooth, stretchy and slightly tacky. Do not add extra flour.

Place dough in a lightly greased bowl, cover and let rise for 1–1 ½ hours, or until doubled.

Meanwhile, portion 180g Nutella into 8 portions and freeze for 30–45 minutes.

Divide dough into 8 pieces. Flatten each piece, place a frozen Nutella portion in the center, then pinch the dough closed. Turn seam-side down and roll into a smooth ball.

Place on a parchment-lined baking sheet, cover and let rise for 45–75 minutes, until very puffy.

Preheat oven to 350°F (175°C). Brush buns with egg wash and bake for 18–22 minutes, until golden brown. Tent with foil if browning too quickly.

Brush the hot buns generously with melted butter. Let cool for 10–15 minutes, then tear one open and enjoy that gooey Nutella center.