In a small jar, mix the sourdough starter, flour, and tepid water until you have a paste. Cover it and leave it out at room temperature for 6 to 8 hours, or overnight.

In a large mixing bowl, combine the levain, warm water, and the two flours. Stir until a shaggy dough forms.

Knead the dough until all the flour is incorporated. Let this sit covered for 1 hour for autolyse.

Sprinkle the salt over the dough and gently knead to incorporate it.

Cover the dough and let it rest for 45 minutes.

For added strength and texture, lightly spray your work surface with water and stretch the dough gently into a thin sheet.

Create folds by lifting and folding the dough over itself four times in a clockwise motion. Rest for 30 minutes and repeat this process three more times every 45 minutes.

After the folds, let the dough rise undisturbed in a warm place for about 2 hours until puffy and bubbly.

Line a proofing basket or bowl with a clean kitchen towel dusted heavily with flour.

Turn the dough out onto a floured surface, shape it into a rectangle, and fold it into a log. Place it seam side up in the basket, cover, and let it proof in the fridge overnight.

Preheat your oven to 475°F (245°C) with a dutch oven inside for 40 minutes.

Cut a piece of parchment paper, dust with flour, and gently turn your loaf onto it. Score the top if desired.

Remove the hot dutch oven, place the loaf inside using the parchment, and cover. Bake for 25 minutes.

Uncover and reduce the temperature to 450°F (232°C) for another 20 minutes, until golden brown.

Cool for at least 2 hours before slicing.