In a bowl, mix 90g of sourdough starter with 385g of warm water until well combined. Set aside.

In a larger bowl, combine 520g of flour and 8-10g of salt.

Add the wet mixture to the dry ingredients and mix until incorporated. The dough should be slightly sticky.

Let the dough rest for 30 minutes.

Perform a series of stretch and folds, resting the dough for 30 minutes between each set, until it becomes more rigid and shaped.

After the final fold, let the dough rest and rise in a warm spot for 8-12 hours, covered with a warm, damp towel.

Cut the cheddar cheese into small cubes and dice the jalapeño.

Sprinkle the cheese cubes and diced jalapeño onto the dough and incorporate them by folding the dough onto itself.

Place the dough back in the bowl, cover with a towel, and refrigerate for 1 hour.

Preheat the oven to 450°F (232°C) with the Dutch oven inside to heat.

Shape the chilled dough, place it on parchment paper, and score the top with a sharp knife.

Carefully transfer the dough with parchment paper into the hot Dutch oven, cover with the lid, and bake for 20-25 minutes.

Remove the lid and bake for an additional 20-25 minutes, or until the crust is golden brown.

Allow the bread to cool on a wire rack before slicing.