After at least 8 hours soaking in the refrigerator, drain and discard the soaking water. Cover the beans generously with fresh water in a large pot and bring to a full rolling boil. Boil for 30 minutes, topping up with hot water as necessary to keep them covered. Drain, then add the measured broth, bay leaf, halved onion and smashed garlic. Simmer for about 30–45 minutes more, or until every bean is fully tender. Older beans may take longer. Remove and discard the bay leaf and halved onion; leave the soft garlic in the broth.

While the beans simmer, heat the vegetable-base oil in a large oven-safe casserole over medium heat. Soften the diced onion, carrots and celery for 8–10 minutes. Add the minced garlic, tomato paste, paprika, fennel, thyme and rosemary and stir until fragrant. If using wine, add it now and simmer briefly, scraping the bottom. Season lightly with salt and pepper.

Heat the mushroom portion of oil in a separate skillet. Add the sliced mushrooms and cook until their moisture evaporates and their edges brown, about 8–10 minutes or longer if needed. Stir in the tamari and balsamic vinegar.

Heat the oven to 375°F (190°C). Add the fully cooked beans, their flavorful broth and the browned mushrooms to the vegetable base. Simmer gently for 15–20 minutes. Taste for salt. The beans should sit in a generous, lightly thickened broth; add water if the pot looks dry, or simmer uncovered if very soupy.

Mix the breadcrumbs with their measured oil, parsley, minced garlic and lemon zest. Scatter over the beans. Bake uncovered for 25–30 minutes, until bubbling around the edges and the crust is golden. Rest for 10 minutes before serving. The filling should remain moist beneath the crisp top.