1.In a large Dutch oven or heavy pot, heat oil over medium-high. Add sausage and cook, breaking up meat with a wooden spoon, until golden brown, about 5 minutes. Add celery and onion and cook until softened, about 5 minutes. Add lentils, broth, and 1/2 cup water and bring to a boil. Reduce to a rapid simmer, partially cover, and cook until lentils and vegetables are tender, 25 minutes. 2.Add kale and season with salt. Return soup to a rapid simmer, cover, and cook until kale wilts, about 5 minutes. Remove soup from heat, stir in vinegar, and season with salt and pepper.