In a large mixing bowl, whisk together the warm water, sourdough discard, instant yeast, and honey until smooth and well combined. Add the bread flour and salt and mix with a dough whisk or your hands until no dry spots remain. The dough will be sticky and shaggy.

Cover the bowl and let the dough rest for 15 minutes. This brief rest allows the flour to hydrate and makes the dough easier to work with.

Perform 3 rounds of stretch and folds, spaced 15 minutes apart (over the next 45 minutes). For each round, grab one edge of the dough, stretch it up, and fold it over itself. Rotate the bowl and repeat 3–4 times per round until the dough tightens slightly.

Lightly oil the bowl with olive oil. Cover with a damp towel or lid and let the dough rise in a warm spot for 1 to 1½ hours, or until noticeably puffed and airy (it does not need to double).

Prepare the pan.

Pour 50 g olive oil into a 10×15-inch baking sheet or 9×13-inch casserole dish, making sure the bottom is well coated.

Transfer the dough to the oiled pan. Gently stretch it toward the corners and lightly dimple the surface with oiled fingers (don’t force it to fill the pan yet). Cover and let rise for 1–2 hours. This dough is very forgiving—longer is fine if your kitchen is cool.

Preheat the oven to 425°F, then reduce the temperature to 375°F just before baking.

Drizzle the remaining ~25 g olive oil over the dough. Dimple deeply with your fingertips, stretching gently as needed so the dough fills the pan. Sprinkle evenly with about 1 tablespoon flaky sea salt.

Bake for ~30 minutes, or until the focaccia is deeply golden on top with crisp edges.

Let cool slightly in the pan, then slice and serve warm or at room temperature.