Begin by soaking the cannellini beans in a large bowl of water with a pinch of salt. Allow them to soak overnight.

In a pot, bring fresh water to a boil over medium-high heat. Add in the soaked cannellini beans and let them boil for 3–4 minutes, then drain again.

In a large soup pot, heat the olive oil over medium-high heat. Once shimmering, stir in the chopped onion and minced garlic. Sauté until the onion is soft and golden, about 5–7 minutes.

Add the parboiled cannellini beans to the pot along with the water or vegetable stock. Bring the mixture to a rolling boil, stirring occasionally.

Reduce the heat to medium-low, partially cover the pot with a lid, and let the soup simmer for about 2 hours. Stir occasionally to prevent sticking.

Once the beans are tender, add in the sliced carrot and chopped celery. Season with salt and pepper to taste. Cook for an additional 20–30 minutes until the vegetables are softened.

Stir in the zest and juice of the lemon before serving. Serve hot.