Rainbow Swirl Sourdough Milk Bread

1. The Night Before, Sweet Starter – Mix together all the together. Cover and let ferment overnight until doubled or tripled and at peak activity.
2. The Next Morning Tangzhong — In a small saucepan whisk together all the ingredients. Cook over medium-low heat, whisking constantly, until the mixture reaches 150°F (65°C) and thickens into a smooth paste. Transfer to a bowl and cool completely before using.
3. Dough Ingredients — Add everything to the bowl of a stand mixer except the oil. Mix on low speed for 5 minutes, until all of the flour is hydrated and no dry spots remain. Cover and let the dough rest for 30 minutes. Add the oil. Continue mixing with the dough hook for about 10 minutes, or until the dough is smooth, elastic, and nearly reaches a full windowpane.
4. Divide & Color — Divide the dough evenly into 6 pieces. Knead each dough until the color is fully incorporated. Continue kneading each dough until smooth and evenly colored (it may be necessary to add small amounts of milk ½ tsp at a time to each to evenly color dough).
5. First Rise — Cover the dough balls and allow them to rise until they are 1½–2 times their original size.
6. Shape — Roll each dough into a rectangle approximately 4 inches wide and the length of your loaf pan. Arrange the colors in rainbow order, overlapping each rectangle by about half an inch with the next color. Roll the layered dough into a tight log. Place into a greased 9×5-inch loaf pan.
7. Final Proof — Option 1: Overnight Refrigerator Proof. Cover the loaf and refrigerate overnight. The next day, remove from the refrigerator and allow it to proof until the dough rises about 1 inch above the rim of the loaf pan.
7. Final Proof — Option 2: Room Temperature Proof Cover and let proof at room temperature for approximately 10 hours, or until the dough rises about 1 inch above the rim of the pan.
8. Bake — Bake at 350°F (177°C) for 40–45 minutes, or until the loaf is deep golden brown and reaches an internal temperature of 200–205°F. If the top begins browning too quickly, loosely tent with foil during the last 10–15 minutes of baking. Immediately remove the loaf from the pan and cool completely on a wire rack. Allow the bread to cool for at least 1 hour before slicing.
9. Baker’s Tips — Natural fruit and vegetable powders absorb moisture differently. If one dough feels dry after adding the powder, knead in a few drops of milk until it matches the consistency of the other doughs. Avoid using excess flour while rolling the colored layers so they stick together well.