Dissolve salt in 4 quarts cold water in large container. Add beans and soak at room temperature for at least 8 hours or up to 24 hours. Drain and rinse well.
Adjust oven rack to lower-middle position and heat oven to 250 degrees. Cook oil and pancetta in Dutch oven over medium heat, stirring occasionally, until pancetta is lightly browned and fat has rendered, 6 to 10 minutes. Add carrots and celery and cook, stirring occasionally, until softened and lightly browned, 10 to 16 minutes. Stir in beans, broth, water, Parmesan rind, and bay leaves and bring to boil. Cover, transfer pot to oven, and cook until beans are almost tender (very center of beans will still be firm), 45 minutes to 1 hour.
Remove pot from oven and stir in kale and tomatoes. Cover, return pot to oven, and cook until beans and greens are fully tender, 30 to 40 minutes.
Remove pot from oven and submerge rosemary sprig in stew. Cover and let sit for 15 minutes. Discard Parmesan rind, bay leaves, and rosemary sprig and season stew with salt and pepper to taste. If desired, use back of spoon to press some beans against side of pot to thicken stew. Serve, passing extra oil and grated Parmesan separately.
