In a large Dutch oven or heavy pot,heat oil over medium-high. Add sausageand cook, breaking up meat witha wooden spoon, until golden brown,about 5 minutes. Add celery and onionand cook until softened, about 5 minutes.Add lentils, broth, and ½ cup waterand bring to a boil. Reduce to a rapidsimmer, partially cover, and cook untillentils and vegetables are tender,25 minutes.
Add kale and season with salt.Return soup to a rapid simmer, cover,and cook until kale wilts, about5 minutes. Remove soup from heat,stir in vinegar, and season withsalt and pepper.
