Make the tangzhong: Bring water to a boil in a medium saucepan. Remove from heat and add saffrom and turmeric. Steep for 15 minutes. Add milk and flour. Whisk until combined and no lumps remain. Place saucepan over medium heat and cook mixture, whisking constantly, until it thickens, about 1-2 minutes. Set aside to cool.
Make the dough: While the tangzhong is cooling, begin preparing the rest of the ingredients for the dough. Combine yeast, salt, sugar and flour in the bowl of a stand mixer. Whisk briefly by hand to combine.
Attach the dough hook to the mixer. Add melted and cooled butter, slightly warm milk, egg and the cooled Tangzhong (it can be slightly warm to the touch) to the dry ingredients. Mix on medium low until fully combined.
Increase mixer speed to medium and knead mixture for 3-4 minutes or until dough is slightly tacky but not sticky and clears the side of the bowl. Add raisins and continue to knead until they are evenly distributed throughout the dough. You can also mix and knead the dough by hand but it will take longer, more like 8-10 minutes.
Cover bowl with plastic wrap and allow the dough to rise for an hour or until 1 ½ or 2 times its original size. The time will largely depend on the temperature of your kitchen.
Once the dough has risen, preheat oven to 350 degrees and adjust oven racks so that they are in the upper and lower middle positions. Line two baking sheets with parchment paper. Remove the dough from the bowl and place it onto a clean countertop. Roll out with a rolling pin until it is in the shape of a rectangle that is about 16 by 6 inches in size. The dough should be smooth enough that you do not need to add flour during the rolling process. If yours is sticking the rolling pin, however, sprinkle a little flour over the dough as necessary to prevent this from happening.
Using a pizza wheel, cut the folded dough lengthwise into 16 one inch strips. Cover with plastic wrap.
Working with one piece of dough at a time and keeping the rest of the dough covered, roll and stretch the strip of dough between the palms of your hands and the countertop into a 16 inch rope. Coil the ends of the rope in opposite directions creating an “S” shape. Place bun onto prepared baking pan. Repeat with remaining dough, spacing buns about 2 ½ inches apart with 8 buns on each baking pan. Cover with plastic wrap and let rise for 30-45 minutes.
Meanwhile, make the egg wash. Whisk the egg and water together in a small bowl. Once the buns have risen and are ready to go into the oven, remove plastic wrap and gently brush the surface of each bun with the egg wash Sprinkle pearl sugar over the top of each bun.
Bake buns for 15-20 minutes or until golden brown, switching and rotating the pans halfway through the baking time. Cool slightly on a wire rack and serve warm. Buns are best when eaten the day they are made.
Don't coil the dough too tightly around itself when create the "S" shapes. The dough will continue to rise so it's helpful if it has a little "space" to expand.