Mix the dough. Whisk flour, salt, and instant yeast in a large bowl. Add sourdough discard and warm water. Stir with a wooden spoon or your hands until no dry flour remains and a rough, shaggy dough forms. Do not overmix.
Oil and cover. Drizzle olive oil over the dough; turn it to coat all sides. Cover the bowl tightly with plastic wrap or a kitchen towel.
First rise. Set the bowl in a warm spot until the dough doubles in size — 1 to 2 hours. Use your oven with just the light on if your kitchen is cool.
Preheat Dutch oven. Put your Dutch oven with lid into the oven. Preheat to 425°F (220°C) for at least 30 minutes.
Shape the loaf. Flour your hands and work surface lightly. Turn dough out, fold each side into the center, pinch the seam, flip seam-side down. Cup your hands around it and drag gently toward you a few times to build a round, tight shape. Place on parchment paper.
Second rest. Cover loosely and rest 30 minutes while the oven finishes heating. Just before baking, score a cut ¼ inch deep across the top with a sharp knife.
Bake covered. Lower dough (parchment and all) into the hot Dutch oven. Put the lid on. Bake 40 minutes — the steam inside gives the bread a full rise.
Bake uncovered. Remove the lid. Bake 5–10 more minutes until the crust is deep golden brown. Internal temp should read at least 200°F (93°C).
Cool completely. Lift out using the parchment paper. Rest on a wire rack at least 30 minutes before slicing — cutting too early makes the inside gummy.