In a small bowl, whisk together the dark brown sugar, ground cinnamon, and 1 tablespoon of water until it forms a thick, wet paste. Set aside.

In a large mixing bowl, whisk the 350g of warm water and active starter together. Add the bread flour and whole wheat flour.

Mix until a shaggy dough forms.

Cover and let rest for 45 minutes to autolyse.

Sprinkle the sea salt over the dough.

Pour the melted butter and honey over the top. Dimple it in with wet fingers and perform a series of stretch and folds for about 3-5 minutes until the dough builds initial tension and absorbs the liquids.

Cover and rest for 30 minutes.

Turn the dough out onto a lightly misted counter. Gently stretch the dough out into a large, thin rectangle (the lamination stage). Using a silicone spatula or your hands, spread the cinnamon-sugar paste evenly across the entire surface of the stretched dough, leaving a small 1-inch border around the edges.

Carefully fold the dough into thirds (like a letter), then roll it up tightly.

Place it back in the bowl, cover, and rest for 30 minutes.

Perform 3 more sets of coil folds spaced 30 minutes apart to continue building strength.

After the last fold, let the dough rest untouched until it has increased in volume by about 40-50%, shows bubbles on the surface, and feels airy.

Turn the dough onto an un-floured surface. Shape it into a tight oval (batard) or a round boule, being careful not to tear the outer skin where the cinnamon might leak out.

Place it seam-side up into a rice-floured banneton. Cover the banneton securely and transfer to the refrigerator for 12 to 16 hours for the cold retard.

Preheat your oven to 500°F (260°C) with a Dutch oven inside for at least 45 minutes.

Turn the dough out onto parchment paper, score it carefully, and transfer it to the hot Dutch oven.

Drop an ice cube under the parchment for extra steam, cover, and bake for 20 minutes.

Remove the lid, reduce the oven temperature to 450°F (230°C), and bake for an additional 20-25 minutes until the crust is deeply caramelized.

Cool completely on a wire rack before slicing.