In a large mixing bowl, combine the bread flour and lukewarm water. Mix until a rough dough forms. Cover with a damp towel and let rest for 30 minutes (autolyse).
Add the active sourdough starter and salt to the dough. Mix thoroughly until fully incorporated.
Add the shredded cheddar cheese and chopped jalapeños to the dough. Fold them in evenly using your hands or a dough scraper.
Perform a series of stretch and folds every 30 minutes for 2 hours (4 sets total) to develop gluten. Keep the dough covered between folds.
After the last stretch and fold, cover the dough and let it ferment at room temperature for 3 to 4 hours, or until it has increased in size by about 50%.
Lightly flour a clean surface and gently shape the dough into a tight loaf. Place it seam-side down into a greased 9×5 inch loaf pan.
Cover the loaf pan with a plastic wrap or damp towel and refrigerate overnight (8-12 hours) for a cold proof.
Preheat the oven to 230°C (450°F). Place a baking stone or inverted baking sheet on the middle rack while preheating.
Remove the loaf from the refrigerator and let it rest at room temperature for 30 minutes.
Score the top of the loaf with a sharp knife or lame.
Place the loaf pan on the preheated baking stone or sheet and bake for 20 minutes.
Reduce the oven temperature to 190°C (375°F) and continue baking for another 20 minutes, or until the crust is golden brown and the internal temperature reaches 95°C (203°F).
Remove the bread from the oven and let it cool in the pan for 10 minutes. Then transfer the loaf to a wire rack and cool completely before slicing.