Open dried cannellini beans and sort out any stones or grit. Put into a large bowl and fill with at least enough water to cover the beans by two inches. Cover and leave overnight.
The Next Day
Drain the water from cannellini beans and rinse.
Add oil to a dutch oven and preheat over medium-high. Add the tasso and sear, stirring often until all sides have begun to color. Remove and set aside.
Add the onion and cook, stirring often, until it is translucent and starting to brown. About 5 minutes. Add chopped celery, bell pepper, and serrano and continue cooking an additional 5 minutes. Add the garlic and cook, stirring constantly, an additional minute.
Add beans, tasso, chicken stock, and seasonings. Bring to a boil, then reduce heat and simmer for 2 to 2 1/2 hours, until the beans are tender.Smash about a quarter cup of beans up against the side of the pot and stir back in. Simmer for an additional 5 minutes.
Taste for salt. Add more if necessary. Serve with a big chunk of homemade cornbread on the side.