Mix: In a small jar, mix 1/4 cup warm water (95F), 1 tbsp active sourdough starter, and whisk until milky. Then, add the 1/2 cup unbleached all-purpose flour and mix well for 1-2 minutes to incorporate the starter well.

Leave at room temperature (70℉) for 10+ hours or until the top of the starter looks bubbly and the volume at least doubles. If the starter doesn't bubble on top and double in size within 10-12 hours, it could mean the starter is weak.

In that case, feed the starter as described in step 1 a time or two or until the starter ripens in under 10-12 hours.

Mix the ingredients:

To a large bowl, add 1 3/4 cups warm water (90F - 95°F). Stir in 1/3 cups sourdough starter from the step above from the night before. Mix well until the water is milky.

Add 1 tbsp kosher salt and 4 cups unbleached all-purpose flour and stir with a wooden spoon to moisten the flour.

Mix the dough:

Then, use your hands to mix everything until a wet dough forms. Clean off the sides of the bowl with a firm rubber spatula. Clean your hands with the dull side of the butter knife and add it to the dough.

Shape into a rough taught ball:

Wet your hands, shape the dough into a rough ball (this is easily done by folding the dough in half until it's to tight to fold again).

Cover the bowl with plastic wrap or a wet kitchen towel. Leave it at room temperature or in a warm place until the dough almost doubles in size, about 6-10 hours.

The dough needs to be in a relatively warm area, otherwise it might take a lot longer to rise. The oven with just the light on is a good place to leave the dough in.

Once the dough almost doubles dust the top of the dough lightly with flour. Turn the bowl over on the table, and with lightly floured hands, help the dough out of the bowl.

Next, keep stretching and folding the dough with floured hands to build tension. Here's how:

Stretch the dough into as large a rectangle as it stretches without tearing. Fold the dough into thirds, envelope style. Fold both sides towards the middle, forming a square/rectangle.

Stretch it out again. Fold it into thirds (envelope style), and roll it into a tight roll.

Pinch the sides of the roll for even ends and roll the dough against an unfloured counter, pushing and moving the dough towards yourself as you rotate it to form a smooth ball. If you handle the dough with lightly floured hands the dough should not feel too sticky. Dust the ball with flour.

All this stretching and folding builds strength, redistributes air pockets, and aligns gluten strands in the dough for an even crumb in the bread.

Dough that rises under tension (tension is created with strong gluten formation) will have a more open crumb.

Line a bowl with a clean cotton kitchen towel (preferably cotton). Liberally dust with flour. Add the dough ball seam side up. Pinch the seam together once more to create a taught ball. Dust with flour if you wish.

Cover with a towel and leave at room temperature (70F) or in the oven with the light on for 2-3 hours or until the dough increases by about 30% and becomes puffy. This dough will continue rising in the fridge overnight.

If planning to bake the same day - proof until about 50% increase.

Do not over-proof or the dough will become runny, stick to the towel and bake into a flat loaf. Once the dough overproofs there's no going back, you'll just have to bake it and hope for the best.

Finger poke test:

Ready: If you press into the dough with a finger about 1 inch deep, the dough will slowly spring back and still leave a slight indent.

Leave to rise a little longer: If the indentation bounces back fast.

Overproofed: If it doesn't bounce back at all, it's over-proofed.

At this point, you can either bake the bread or place it in the fridge for cold fermentation.

Cold fermentation will improve texture and flavor, and the oven will spring.

Place the bowl into a plastic bag or cover with a disposable shower cap to prevent drying out.

Refrigerate overnight.

Preheat the oven:

Adjust the oven rack to one just below the middle.

Place the Dutch oven with the lid on top.

Preheat the oven to 450F for 30 minutes to 1 hour.

Score the bread:

5 Minutes before the oven is preheated, remove the dough from the fridge.

Remove the dough from the plastic bag.

Turn the dough out of the bowl on to a piece of parchment paper.

With a sharp serrated knife make a 5-inch cross on top of the dough going about 1/2 inch deep.

Transfer the dough into the preheated Dutch oven by pulling on the parchment paper.

Add ice:

To keep the crust thin add 1-2 cubes of ice behind the parchment paper. The steam will keep the crust from hardening for longer, allowing the bread to open up better.

Quickly, cover with a lid to trap in steam.

Bake for 20 minutes with the lid on.

Then, remove the lid and bake for another 20-25 minutes or until golden color. The internal temperature of the bread should read 205℉ - 210℉.

Remove from the Dutch oven and allow to cool on a cooling rack for several hours before cutting.