01 - Combine active sourdough starter, lukewarm water, and brown sugar in a large mixing bowl. Stir continuously until sugar completely dissolves.
02 - Add bread flour, whole wheat flour, cinnamon, nutmeg, ginger, and salt to the starter mixture. Mix thoroughly until a shaggy, sticky dough forms.
03 - Gently fold grated carrots, raisins, and nuts into the dough until evenly distributed throughout.
04 - Knead dough gently by hand or with dough hook attachment for 3-4 minutes until ingredients are just combined. Do not overwork.
05 - Cover bowl with damp towel and let dough rest for 30 minutes to allow flour hydration.
06 - Perform 3-4 sets of stretch and folds at 30-minute intervals over 2 hours to develop gluten structure and strength.
07 - Cover and allow dough to rise at room temperature for 4-6 hours until doubled in size.
08 - Shape dough into a tight boule or batard. Place seam-side up in a parchment-lined banneton or bowl.
09 - Cover and refrigerate overnight for 8-10 hours to develop flavor through slow fermentation.
10 - Preheat oven to 450°F with Dutch oven inside for at least 30 minutes to ensure proper heat retention.
11 - Turn dough onto parchment paper. Sprinkle oats and seeds on top if using. Score the loaf with a sharp knife or lame.
12 - Carefully transfer dough into preheated Dutch oven. Bake with lid on for 25 minutes to create steam and oven spring.
13 - Remove Dutch oven lid and continue baking for 20 minutes until crust is deep golden brown and crispy.
14 - Transfer loaf to wire rack and cool completely before slicing to prevent gummy texture.