Sausage and Kale Soup

http://www.marthastewart.com/338115/sausage-and-kale-soup

  • 1 tablespoon olive oil
  • 1 onion, diced
  • 2 garlic cloves, minced
  • 1/4 teaspoon crushed red-pepper flakes
  • 5 waxy potatoes (1 1/2 pounds), peeled and cut into 1/2-inch chunks
  • 3 cans (14 1/2 ounces each) reduced-sodium chicken broth
  • 1 bunch kale (12 ounces), stemmed and shredded
  • 12 ounces smoked chicken sausage, cut into 1/2-inch half moons