Nikuman - Japanese steamed buns

INGREDIENTS

• White and green of 1 spring onion, finely chopped
• 2 teaspoons light soy sauce
• 10g fresh yeast or 1 tablespoon active dry yeast
• 1 teaspoon sesame oil
• 4 ounces cooked pulled (or fresh ground pork)
• 1 cup warm water
• 2 teaspoons finely grated fresh ginger
• 1 large egg, lightly whisked
• 2 teaspoons chili garlic sauce
• 1 tablespoon rice vinegar, for cooking (optional)
• 1/4 cup granulated sugar
• 2 teaspoons granulated sugar
• 2 tablespoons butter (chilled and cut into pieces)
• Portion bread dough - recipe below
• 1 teaspoon salt
• 3 1/4 cups all-purpose flour