In a mixing bowl, combine 350 g of warm water with 100 g of active sourdough starter, stir until fully mixed. Gradually add 25 g of granulated sugar and 500 g of unbleached all-purpose flour, mixing until a shaggy dough forms. Sprinkle 11 g of kosher salt on top, cover the bowl with a towel, and let the mixture rest for 30 minutes.

After the rest, dampen your hands and pinch in the salt, gently shaping the dough. Cover the bowl again and allow it to rest for another 30 minutes. Perform stretch and folds every 30 minutes for a total of two more times. Let the dough bulk ferment at room temperature for about 3-4 hours, or until it becomes visibly puffy and bubbly.

Flour a clean surface and turn out the dough, stretching it into a rectangle approximately 10x15 inches. Evenly sprinkle the surface with 2 tablespoons of ground cinnamon and 135 g of dark brown sugar. Fold the dough into thirds like a letter and roll it tightly into a boule shape. Transfer the dough into a proofing basket lined with a floured towel and refrigerate for 2-3 hours, or until it has slightly puffed up.

Preheat your Dutch oven to 450°F. Carefully lift the dough from the proofing basket and place it onto parchment paper. With a sharp knife, score the top to allow steam to escape during baking. Lower the dough into the preheated Dutch oven, cover it, and bake for 25 minutes, then uncover and bake for an additional 18-20 minutes until the bread is golden brown and sounds hollow when tapped.

Once baked, carefully transfer the bread to a wire rack and allow it to cool for at least 2 hours. After cooling, your Cinnamon Brown Sugar Sourdough Bread will be ready to slice and enjoy.