In a large mixing, combine the warm water and active sourdough starter. Use a whisk or Danish dough whisk to dissolve the sourdough starter into the water. Add the 25 g of granulated sugar to the mixture, and whisk to thoroughly incorporate.

Add the unbleached flour to the mixing bowl, and use a wooden spoon or Danish dough whisk to incorporate the flour. When it becomes too thick to stir, use your clean hands to bring the dough together. The dough will be super shaggy, but that's ok. I like to use my bench scraper to scrape the excess dough off of my hands and back into the bowl. Scrape down the sides of the bowl as well, and sprinkle the kosher salt on the surface of the dough. Cover the bowl with plastic wrap or a clean disposable shower cap, and let the dough rest at room temperature for 30 minutes.

After 30 minutes, use damp hands to throughly pinch the salt into the dough. This will take a couple of minutes. Use your hands to bring the dough together into a round shape, and cover the dough again, and let it rest for another 30 minutes.

Stretch and fold the dough: remove the bowl cover, and gently stretch/pull one side of the dough up, and fold it over the ball of dough. Rotate the bowl 90°, and stretch the next side of the dough up, and fold it over. Work your way around the ball of dough until all of the sides have been stretched and folded. Lift the ball of dough up, and plop it over upside down back into the bowl. Cover the bowl again, and let the dough rest for another 30 minutes.

Repeat this process another 2 times, stretching and folding the dough every 30 minutes. After the last stretch and fold, cover the dough again, and let it bulk ferment at room temperature for 3-4 hours, or until it is puffy, almost doubled in size, and there are small air bubbles on the surface of the dough.

Very lightly flour your work surface, and pour the risen dough out onto the work surface. Gently stretch the dough out into a large rectangle, about 10x15". Generously sprinkle the surface of the dough with cinnamon, leaving a 1/2" border around the perimeter. Next, sprinkle 2 tablespoons of brown sugar on top of the cinnamon. Use your palms to gently press the brown sugar down into the dough.

Fold the top 1/3 of the dough down into the center midline. Sprinkle on more brown sugar and cinnamon, leaving a small border. Fold the bottom 1/3 of the dough over the other 2 layers, like a letter fold. Sprinkle on more cinnamon and sugar, and gently pat the brown sugar into the dough. Carefully roll up the dough, enclosing the brown sugar and cinnamon, and use your hands to gently push and pull the dough around, forming a round boule shape.

The syrupy brown sugar can leak out while the dough's proofing, so I line my proofing baskets with a tea towel, and dust it generously with flour or rice flour. Place the shaped loaf into the prepared proofing basket, cover the loaf with a clean disposable shower cap (to prevent it from drying out), or place it in a plastic bag - let the dough proof in the fridge for 2-3 hours.

Place a large Dutch oven (with the lid on) into the middle rack of the oven, and preheat the oven to 450℉. Once the oven has come up to temperature, let it continue to heat up for another 25-30 minutes. Remove the dough from the fridge while the oven is preheating.

Using oven mitts, carefully remove the Dutch oven from the oven, and remove the lid. Gently pour the dough out onto a piece of parchment paper, and score the top of the loaf to allow the steam to release.

Lift the parchment paper with the dough on it, and lower it into the preheated pot. Place the lid on top, and place the Dutch oven back into the oven. Bake for 25 minutes.

After 25 minutes, remove the lid from the pot, and bake for another 18-20 minutes until the curst is deeply golden brown/mahogany color. Remove the loaf from the Dutch oven, and allow it cool completely on a baking rack for at least 2 hours. Enjoy!