In a large Dutch oven or soup pot, heat the olive oil over medium-high heat. Once hot, add the sausage and cook for 5 minutes or until the sausage is browned, breaking up the sausage up with a wooden spoon as it cooks. Transfer the sausage to a plate and set aside.
Add the onion, celery, carrots, and cook for 5 minutes until softened, stirring occasionally. Add the garlic and cook for 1 minute.
Add 2 cans of the white beans, Parmesan rind, Italian seasoning, salt, pepper, and crushed red pepper flakes.
Pour in the broth and bring the soup to a boil, then reduce the heat to low and simmer for 20 minutes, stirring occasionally.
Remove the Parmesan rind. Use an immersion blender to blend the soup in the pot to make it more creamy. Alternatively, you can use a blender or food processor to puree the soup in batches, leaving some texture. Return the soup to the pot after blending.
Add the sausage back to the pot. Stir in the remaining can of beans, kale, lemon juice, and parsley. Allow the soup to cook for a few more minutes. Stir in Parmesan cheese. Taste and adjust seasonings, if necessary.
Ladle the soup into bowls and serve with extra Parmesan cheese, if desired.
Notes
Store leftovers in an airtight container in the fridge for up to 4 days. You can also freeze the soup for up to 3 months.