1. Combine Wet Ingredients and Discard: In a large mixing bowl, whisk together the warm water and sourdough discard until well combined. The discard doesn’t need to be perfectly dissolved, just mostly incorporated.

2. Add Dry Ingredients: Add the all-purpose flour, salt, and optional instant yeast to the wet mixture. Use a sturdy spoon or your hands to mix everything together until a shaggy dough forms and no dry streaks of flour remain. It will be sticky, which is normal for a high-hydration dough.

3. First Rise (Bulk Fermentation): Lightly grease another large bowl with olive oil. Transfer the dough to the greased bowl, turning it once to coat. Cover the bowl with plastic wrap or a damp kitchen towel and let it rise in a warm spot for 2-4 hours, or until it has visibly increased in size by about 50-75%. If you used instant yeast, it might rise faster.

4. Shape the Batard: Gently turn the dough out onto a lightly floured surface. Avoid deflating it too much. Gently stretch and fold the dough into a rectangular shape. Then, starting from one of the longer sides, roll the dough tightly into a log, pinching the seam closed as you go. Gently cup your hands around the ends and roll it slightly to create a batard (oval) shape.

5. Second Rise (Proofing): Lightly flour a proofing basket (banneton) or a bowl lined with a floured kitchen towel. Carefully transfer the shaped dough, seam-side up, into the prepared basket/bowl. Cover loosely with plastic wrap and let it proof at room temperature for 1-2 hours, or until it looks puffy and has increased in size. Alternatively, for a deeper flavor and easier baking schedule, you can refrigerate it overnight (8-12 hours).

6. Preheat Oven and Dutch Oven: About 30-45 minutes before baking, place a Dutch oven with its lid into your oven and preheat to 450 F (232 C). Getting the Dutch oven very hot is crucial for a great crust.

7. Score and Bake: Carefully remove the hot Dutch oven from the oven. Gently invert the dough from the proofing basket into the hot Dutch oven. Using a sharp knife or a bread lame, score the top of the dough with a few shallow cuts (about 1/2 inch deep) – this helps the bread expand beautifully. Place the lid back on the Dutch oven and bake for 30 minutes.

8. Final Bake and Cool: Remove the lid from the Dutch oven and continue baking for another 15-20 minutes, or until the crust is deeply golden brown and sounds hollow when tapped on the bottom. Carefully remove the bread from the Dutch oven and transfer it to a wire rack to cool completely before slicing. This cooling step is vital for the crumb to set properly.