1. Combine Wet Ingredients and Starter: In a large mixing bowl, combine the active sourdough starter (or discard) with the warm water. Stir gently with a wooden spoon or spatula until the starter is mostly dissolved and well incorporated into the water. This creates a milky, bubbly mixture.

2. Add Dry Ingredients: Gradually add the flour and salt to the wet mixture. Mix until a shaggy dough forms and all the flour is hydrated. It doesn’t need to be perfectly smooth at this stage. Cover the bowl with a damp kitchen towel or plastic wrap and let it rest for 30 minutes. This resting period, called autolyse, helps the flour absorb water and develop gluten.

3. Incorporate Inclusions: After the rest, uncover the dough. Gently fold in the shredded cheddar cheese and diced jalapenos until they are evenly distributed throughout the dough. Try not to overmix at this stage; just ensure the inclusions are well integrated.

4. Bulk Fermentation (First Rise): Lightly oil a clean bowl with olive oil. Transfer the dough to the oiled bowl, turning it once to coat. Cover the bowl again and let it ferment at room temperature (around 70-75 F) for 8-12 hours, or until it has visibly increased in size and appears bubbly and alive. During this time, perform 3-4 sets of “stretch and folds” every 30-60 minutes during the first 2-3 hours of fermentation. To do this, gently grab a portion of the dough, stretch it upwards, and fold it over itself. Rotate the bowl and repeat 3-4 times.

5. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Carefully shape it into a round or oval loaf. Avoid deflating the dough too much. If using a banneton (proofing basket), lightly flour it and place the shaped dough seam-side up. If not, place it on a piece of parchment paper.

6. Proofing (Second Rise): Cover the shaped dough loosely with plastic wrap or a damp towel and let it proof at room temperature for 2-4 hours, or until it looks puffy and springs back slowly when gently poked. Alternatively, you can cold proof it in the refrigerator overnight (8-12 hours) for a deeper flavor development.

7. Preheat Oven and Bake: About 30 minutes before baking, preheat your oven to 450 F (230 C) with a Dutch oven or baking stone inside. Carefully remove the hot Dutch oven from the oven. Gently transfer the dough into the hot Dutch oven (or onto the baking stone). Score the top of the dough with a sharp knife or razor blade. Cover the Dutch oven and bake for 30 minutes.

8. Finish Baking: After 30 minutes, remove the lid from the Dutch oven. Reduce the oven temperature to 400 F (200 C) and continue baking for another 15-25 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210 F (93-99 C).

9. Cool Completely: Carefully remove the loaf from the Dutch oven and transfer it to a wire rack to cool completely before slicing. This is crucial for the internal structure and flavor to set properly. Resist the urge to cut into it too soon!