• Place the starter and 320 grams of water in a large bowl and mix until the starter is dissolved.
• Add the flour and using your hands, mix the flour into the water and starter. Mix until you have a shaggy mass of dough. The dough is going to be wet.
• Cover and let it sit for 30 minutes at room temperature.
• After 30 minutes, add the salt and the remaining water to the dough and with your fingers, squeeze the salt into the dough and mix for about 3 to 4 minutes until you cannot feel the grains.

Bulk fermentation

• Cover the bowl and place it in a draft free environment (like an off oven) and every 45 minutes, do a stretch and fold: wet your fingers and grab a side of the dough, stretch it and fold it over the dough. Turn the bowl 90 degrees and repeat the stretch and fold.
• Repeat until you have stretched and folded all the sides onto the dough. You should do 4 sets of stretch and fold and let the dough sit for 30 minutes after the last set. Meaning the whole bulk fermentation time will be 3 hours and 30 minutes.

Preshape

• Transfer the dough to a floured surface and sprinkle a bit of flour on top so you can handle it. using a bench scraper, cut the dough in half.
• Fold two sides of the dough from left and right to the center and then from top and bottom to the center.
• Next, fold in the corners to the center. Top the dough with flour. Using your bench scraper, lift the dough and flip it so seam side is down. With your hands, push the dough towards yourself, turn 90 degrees and repeat. Do this process 4 times in total. Use a bit more flour if needed. Cover with a kitchen towel and let it rest for 20 minutes. You will start seeing bubble on the surface and sides.

Make the glaze

• Place the flour, water and baking soda in a small pan and bring it to simmer. Cook for 3 to 5 minutes until it thickens. Turn the heat off and set it aside, the glaze will thicken more when cools.
• Final shape
• After the 20 minute rest for the dough, transfer one of the dough balls to a parchment paper and using your hands, flatten it into an oval shape. Let it rest for 30 minutes. Meanwhile, preheat the oven to 480℉ and place a large baking sheet inside the oven on the middle rack. Place a metal baking pan or a cast iron skillet on the lower rack as well.
• After 30 minutes, divide the glaze between the two loaves and spread it over using your fingers. With your finger having the glaze on them, make deep indentations in rows on the dough (this way the dough wouldn't stick to your fingers) and be careful not to tear the dough. Top with sesame seeds.
• Open the oven door and pour ½ cup water into the cast iron skillet or metal baking pan on the lower rack. Transfer the parchment paper with the dough onto the baking sheet on the middle rack and close the oven door. Bake for 9 minutes.
• Take the cast iron skillet or metal baking pan out of the oven and close the oven door. Reduce the heat to 450℉ and bake the bread for another 4 minutes until the top is golden brown.
• Take the bread out of the oven and let it cool for about 30 minutes before cutting it.