Taco Sweet Potato Shepherd's Pie

Cook sweet potatoes in a large pot of boiling water until tender, 10 to 12 minutes. Drain, then return the sweet potatoes to the pot. Cook over medium-low heat until excess moisture is evaporated, 1 to 2 minutes. Remove from heat. Add milk and mash with a potato masher until smooth. Stir in Cheddar, cilantro, lime zest, 1/4 teaspoon salt and pepper; set aside.

Heat oil in a 10-inch cast-iron skillet over medium heat. Add onion, garlic and jalapeño and cook until softened, about 5 minutes.

Add beef and cook, breaking up with a wooden spoon, until browned, about 8 minutes. Stir in tomato paste, chili powder, cumin, coriander and oregano and cook until fragrant, about 1 minute. Stir in broth, scraping up any browned bits. Stir in corn, black beans, bell pepper and remaining 1/2 teaspoon salt; cook until the liquid has nearly evaporated, about 10 minutes. Stir in lime juice.

Preheat broiler to high with rack set 6 inches from element.

Evenly spread the mashed sweet potatoes over the beef mixture in the skillet. Broil until just starting to brown, 7 to 8 minutes. Let the pie rest for 5 minutes before serving.