Heat oil in a medium saucepan over medium heat. Add apple, potato, onion and celery; cook, stirring often, until the onion is translucent, about 5 minutes. Stir in salt, sage, paprika and pepper; cook for 30 seconds. Pour in broth and bring to a simmer. Reduce heat, cover, and gently simmer until the potato is tender when pierced with a fork, 10 to 15 minutes.