Begin by draining the soaked cannellini beans in a colander. In a large pot, cover the beans with fresh water and bring to a boil over medium-high heat. Boil for about 3-4 minutes, then remove from heat and drain again.

In a medium pot, heat 2 tablespoons of high-quality extra virgin olive oil over medium heat. Once hot, add the minced onion and chopped garlic, sautéing them until the onion turns golden and translucent, about 5-7 minutes.

Stir in the prepared beans along with 6 cups of water or vegetable stock into the pot with garlic and onion. Bring the mixture to a gentle boil, then reduce the heat to low, covering the pot partially with a lid. Let it simmer for about 2 hours, stirring occasionally, until the beans are tender and the soup thickens to a creamy consistency.

After the beans have simmered for 2 hours, add the thinly sliced carrot and finely chopped celery to the pot. Season the soup generously with kosher salt and freshly ground pepper. Continue to simmer for another 30-45 minutes, stirring occasionally, until the vegetables are tender and the soup attains a rich, hearty texture.

Just before serving, stir in the zest and juice of one lemon into the pot. Allow the soup to cook for an additional 2 minutes, letting the lemon infuse its acidity throughout. Taste and adjust the seasoning if necessary before ladling into bowls.