Wynn Soo, Barcook Bakery
Make Old Dough. Knead all ingredients together on low speed for 10 to 15 minutes to make a smooth ball of dough that cleans the mixing bowl. Chill for 12 to 14 hours, covered.
Make Tangzhong. Combine flour, salt and sugar in a bowl. Bring water to a boil and pour it into the dry ingredients, stirring to mix well. Let cool to room temperature, then chill overnight, covered.
Make Main Dough. Combine all ingredients except butter and purple sweet potato, and knead on low speed until dough comes together, about 5 minutes.
Knead on high speed for 6 to 7 minutes, until dough develops more elasticity.
Add butter and purple sweet potato dice. Continue kneading dough until it reaches the windowpane stage.
Mix in California Raisins for about 1 minute on low speed to incorporate. Final dough temperature should be about 26°C. Shape dough into a round, cover and let proof for 1 hour.
Divide dough into 10 portions, about 240 g each. Shape into rounds, cover and let rest for 20 minutes.
Have ready 5 non-stick loaf pans, 214 mm long by 122 mm wide by 130 mm deep.
Flatten each dough portion into a long rectangle, let rest for 10 minutes.
Sprinkle about 22 g California Raisins over each rectangle, then roll them up into tight logs. Place 2 logs into each loaf pan.
Let proof for 1 hour, until loaves have filled pans about 80% full.
Preheat oven to 160°C (top element) and 225°C (bottom element).
Brush breads with beaten egg. Slash each bread twice diagonally. Bake for about 34 minutes, until golden brown.
Remove bread from oven and immediately unmould onto a rack to cool.