Brown the ground beef in a large pot or Dutch oven over medium-high heat, breaking it into crumbles, 6 to 7 minutes. Drain off the fat.
Stir in the taco seasoning until the beef is coated, about 30 seconds.
Pour in the salsa and beef broth, then add the dry pasta shells, black beans, and corn. Stir well and bring to a boil.
Reduce to a steady simmer, cover, and cook 12 to 14 minutes, stirring once or twice, until the shells are tender and most of the liquid is absorbed.
Take the pot off the heat and stir in 1 1/2 cups of the cheddar until melted. Top with the remaining 1/2 cup cheddar, cover for 2 minutes so it melts, then serve with cilantro and sour cream.