Cook sausage in a large heavy pot over medium heat, stirring often to crumble, until browned, about 5 minutes. Add onion, celery and garlic; cook, stirring often, until softened, about 6 minutes. Add tomato paste; cook, stirring constantly, for 1 minute. Stir in tomatoes, potatoes, broth, pepper and salt. Bring to a simmer over medium-high heat. Cover; reduce heat to medium and simmer until the potatoes are tender, about 20 minutes.