Drain and rinse the butter beans.
Zest both lemons into a large dutch oven. Then juice just one lemon, setting aside about 3 tablespoons of juice.
Add the heavy cream to the dutch oven and bring it to a slight simmer. Then, whisking constantly, add in 1 tablespoon of butter at a time, adding another as soon as the prior one is combined into the sauce.
Add the beans into the sauce and stir, letting simmer another 5-6 minutes to let the sauce thicken around the beans. Grate in the parmesan and stir to create a smooth and glossy sauce.
Add in the lemon juice, then season with salt and pepper to taste. It shouldn't need much.
Serve on four plates and scatter the parsley on top. Serve warm!