In a 75°F/24°C kitchen, my dough needed about 6 hours to expand by 75%. It proofed about 30 minutes at room temp, then in the refrigerator for 6 hours. The sugar in the filling liquified a bit during this long-ish time, so I recommend a shorter, room temperature only/mainly final proof. You can extend the bulk fermentation with refrigeration instead, if you prefer a long fermentation. If you want to stiffen the dough before scoring and baking, put the proofing basket in the freezer for 20 minutes at the end of the final proof.

Combine the dough ingredients in a large bowl and mix until the dough is smooth. Cover and set aside to rest 20-30 minutes. Do one or more rounds of stretching and folding to strengthen the dough.

Prep the filling by mixing the cinnamon and brown sugar until they're well combined.

Prep your proofing basket either by flouring it or lining it with parchment paper. While proofing, the shaped dough may leak brown sugar-water onto your basket. I washed my liner and basket, which was no big deal, but if you prefer to avoid this, line your proofing basket with a piece of crumpled-and-then-smoothed-out parchment paper. If you put the dough directly in the basket, have it seam up. If you put the dough on parchment paper in the basket, have it be seam down because you won't flip it when transferring to the baking vessel. If your baking vessel is made of unglazed clay and you haven't already embraced the idea of 'seasoning' via stains, make the parchment paper large enough that it also protects your baking vessel.

See the video above for a visual representation of the shaping instructions. When the dough has expanded by about 75%, stretch it out on a lightly floured work surface. Flip the dough to its sticky side if it's snapping back rather than stretching. When the dough is about 16x16 inches, cover it with some of the filling. Now letter-fold one side, pausing to cover the new surface with filling. Letter fold the second side and cover that with filling. Roll the long rectangle you've created into a tube. Pinch the ends closed, flour, and put it in the proofing basket.

Cover and let the dough proof 1-2 hours or until it has expanded a bit (see the photo gallery). Pop the basket in the freezer for 20-30 minutes if you want the dough to be stiffer.

Preheat the oven and baking vessel to 500°F/260°C for 30 minutes.

Score the dough and load it into the baking vessel and oven. Bake covered the entire time (except for internal-temp checks) because the sugar will burning if the bread is uncovered.

Bake at 500°F/260°C for 15 minutes and 450°F/232°C for 20 minutes more or until the internal temperature of the bread is at least 205°F/96°C.