Heat 3-4 tablespoons vegetable stock or water in a large soup pot over low heat, add the onions and allow to cook, stirring occasionally until translucent.

Add the carrots, garlic and celery with a pinch of salt and cook until vegetables are softened, around 10 minutes. Add few tablespoons of vegetable stock if needed and stir to avoid burning.

Pour in the vegetable broth. Add potatoes, tomato cubes, Herbs de Provence seasonings, red pepper flakes, salt and pepper to taste. Stir well. Bring the soup to a boil and allow to cook on medium heat until potatoes are tender.

Add the drained and rinsed beans, reduce the heat to simmer and partially cover the pot. Simmer for 3-4 minutes.

Remove ¼ of the soup and blend until smooth using an immersion blender then return to the pot, stir well, this will help thicken the soup. 

Add the chopped escarole to the soup and simmer for 3-5 minutes, or until the escarole is tender but still bright green.

Adjust seasonings, adding more salt and pepper if needed.

While the soup is simmering make gremolata. Finely chop parsley then zest the lemons and grate the garlic. Sprinkle with salt and mix parsley, lemon zest and garlic. Keep aside until the soup is served.

Serve the soup hot with gremolata sprinkled on top. Stir in lemon juice if desired.