Step 1

Heat the oil in a large saucepan over medium heat. Add the celery and shallots, season with salt and pepper, and cook, stirring occasionally, until soft and fragrant, 2 to 3 minutes. Add the rosemary and cook, stirring, for 1 minute. Pour in the broth and bring to a simmer. Gently add the meatballs to the broth and allow the broth to return to a simmer. Stir in the beans and cook until the meatballs are done and the beans are warmed through, 8 to 10 minutes.

Step 2

Remove the pot from the heat and stir in the mustard greens, letting them cook in the ambient heat of the broth until wilted and tender-crisp, about 3 minutes. Season the soup with salt and pepper and sugar, if you like.

Step 3

Ladle the soup into bowls and serve with rice and lemon wedges on the side for squeezing over each serving.