Simmer beans in 3 times the amount of water as beans with bay leaf, shallot, garlic, salt, pepper, and herbs. Cook until tender, 30 minutes to 1 hour. Strain and cool. This can also be done the day before.
In an oven safe dish, put the cured duck legs skin side up in the oven at 250 F, covered, for 3-4 hrs until tender and falling off the bone. Remove from liquid / duck fat and cool.
Render diced bacon on low until crispy and you have lots of bacon fat in the pan. Strain out the bacon and set aside.
Turn heat up to medium high and cook onion and celery in bacon fat until translucent, then add carrots and garlic a cook until golden.
Deglaze pan with brandy and white wine.
Add bacon, beans, herbs, duck or chicken stock, salt, pepper and bay leaves.
Bring to a simmer and put in the oven at 375 F, uncovered, until some beans break down and create a creamy broth, about 2-3 hours. Beans should be very tender.
In the meantime, pull the duck off the bones and leave in chunks; it is okay for some to be smaller shreds. (Optional: Reserve duck fat and skin to crisp up under the broiler and sprinkle on top as cracklings at end.) Add liquid as needed.
When the beans are just about done, mix in the duck and cook for 10 more minutes.
Take the beans out, season to taste with vinegar, salt, and pepper.
Turn oven to broil, top beans with breadcrumbs and cook until brown.
Sprinkle with duck skin cracklings (optional but encouraged) and chopped scallion.
Serve immediately and don’t forget to remove the bay leaves!