Step 1

Place beans, onion, carrots, and celery in a large pot and add cold water to cover by several inches. Bring to a boil, then reduce heat and simmer very gently until beans are cooked almost all the way through, about 1½ hours. Season with salt and continue to cook, adding more water if needed to keep beans submerged, until tender (outside skin should still be intact), 45–60 minutes. Discard onion, carrots, and celery.

Step 2

Transfer beans and broth to a serving dish or a large bowl; season very generously with salt (start with 2 Tbsp.) and pepper and drizzle with oil.

Step 3

Do Ahead: Beans can be cooked and seasoned 2 days ahead. Let cool; cover and chill. Reheat gently before serving.