Heat a large pot or dutch oven over medium and cook sausage, breaking down into small pieces.
When sausage is mostly cooked/browned, add the chopped onion, leek, rosemary and garlic. Stir to combine and let cook another 5 minutes, adding a pinch of salt and pepper here. Chop the potatoes into 1 inch chunks while you're waiting.
Add chopped potatoes, white beans, and stock, stirring to combine. If you have a parmesan rind lying around, add it now! Not necessary, but does add flavor.
Bring to a boil and then lower to a simmer and cover with the lid slightly ajar. Cook for 20-25 minutes, until potatoes can be pierced easily.
In the meantime, using a bullet or immersion blender, mix one can of drained beans with 3/4 cup filtered water and blend on high until creamy. Set aside.
Remove the parmesan rind from the soup. Add chopped kale (stems removed), lemon juice, and bean purée, stirring to combine. Season with plenty of salt and pepper to taste.
Notes
To Freeze: Wait for soup to fully cool and then store in an air-tight container. Will last up to 2 months in the freezer.