Step 1: Make the Tangzhong
In a small saucepan, whisk together flour, milk, and water.
Cook over medium heat, stirring constantly, until thick and smooth like a paste (about 2–3 minutes).
Let cool slightly before using.

Step 2: Make the Dough
In a large mixing bowl or stand mixer, combine bread flour, sugar, salt, and yeast.
Add egg, warm milk, and cooled tangzhong. Mix on low until combined.
Add softened butter and knead for 10–15 minutes until the dough is smooth and elastic.
It should pull away from the sides but still feel soft and slightly tacky.

Step 3: First Rise
Cover the dough with a towel or plastic wrap.
Let rise in a warm place for 1–1.5 hours, or until doubled in size.

Step 4: Prepare the Chocolate Paste
In a small bowl, mix cocoa powder, sugar, milk, and melted butter until smooth.
Set aside.

Step 5: Roll and Swirl
Punch down the risen dough and turn it out onto a lightly floured surface.
Roll into a rectangle, about 8×14 inches.
Spread the chocolate paste evenly over the dough.
Roll up the dough tightly, starting from the short side, like a jelly roll.
Place seam-side down in a greased loaf pan.

Step 6: Second Rise
Cover and let rise for 45–60 minutes, until puffy and nearly doubled in size.

Step 7: Bake the Bread
Preheat oven to 350°F (175°C).
Brush the top of the loaf with milk or a beaten egg for shine.
Bake for 30–35 minutes until the top is golden brown and the loaf sounds hollow when tapped.
If the top browns too quickly, tent with foil during the last 10 minutes.

Step 8: Cool & Slice
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack.
Cool completely before slicing to reveal the beautiful chocolate swirl.