Heat 2 tablespoons olive oil in a large soup pot or Dutch oven over medium-heat. Add the ground sausage and cook for 5 minutes. Transfer the cooked sausage to a plate and ser aside.
In the same pot used to cook the sausage, add the onion, carrots, and celery. Sauté for 5 minutes until slightly caramelized. Add the garlic and sauté for 30 seconds. Season with Italian seasoning, salt, black pepper, and red pepper flakes.
Pour in the broth, tomatoes, thyme sprigs, and parmesan rind. Bring the soup to a boil, then reduce the heat to low and simmer for 20 minutes, stirring occasionally. Add the sausage back to the soup, along with the white beans, and the kale. Simmer for an additional 2-3 minutes.
Remove the parmesan rind and discard. Finish with lemon zest, a big squeeze of lemon juice, and remaining 2 tablespoons of olive oil. Sprinkle parmesan cheese, if desired. Enjoy!
