In a large mixing bowl, combine 1 ½ cups of warm water with ½ cup of active sourdough starter. Gradually add 4 cups of bread flour and 1 ½ teaspoons of salt, mixing until a shaggy dough forms.

Cover the bowl with a clean kitchen towel or plastic wrap and let the dough rest for 30 minutes.

Perform the stretch-and-fold technique by wetting your hands and grabbing one side of the dough. Stretch it upward before folding it over itself, rotating the bowl and repeating this process for a total of 4 rounds, every 30 minutes.

Once elastic and smooth, gently fold in 1 cup of diced jalapeños and 1 cup of shredded cheddar cheese.

Cover the dough and let it rise in a warm environment until it doubles in size, approximately 1 to 2 hours.

Turn the dough out onto a floured surface and shape it into a round loaf.

Cover the banneton with a kitchen towel and allow the dough to proof at room temperature for about 30 minutes.

Preheat your oven to 450°F (230°C) for at least 30 minutes.

Carefully remove the heated Dutch oven, place the dough inside, and cover with the lid. Bake for 20 minutes, then remove the lid and bake for another 20 minutes until golden brown.

Transfer the loaf to a wire rack, cooling for at least 30 minutes before slicing.