2 pounds sweet potatoes, peeled and chopped (6 cups)
½ cup sour cream
2 tablespoons unsalted butter
½ teaspoon salt, divided
2 teaspoons cornstarch
1 cup unsalted beef broth
1 pound lean ground beef
2 medium carrots, halved lengthwise and thinly sliced into half-moons
1 medium yellow onion, chopped
3 medium cloves garlic, finely chopped
2 tablespoons tomato paste
1/2 tsp dried oregano
1/2 tsp paprika
1/2 dried thyme
1 ½ cups frozen peas
1 tablespoon Worcestershire sauce
1 teaspoon ground pepper
Preheat oven to 425°F. Place sweet potatoes in a large saucepan; add water to cover by 1 inch. Bring to a boil over high heat. Reduce heat to medium; simmer, undisturbed, until forktender, 10 to 12 minutes. Drain the sweet potatoes and return to the pan. Mash with a potato masher until mostly smooth. Stir in sour cream, butter and 1/4 teaspoon salt. Set aside. Whisk cornstarch and broth in a small bowl; set aside. Heat a large ovenproof skillet over medium-high heat. Add ground beef and cook browned, breaking up the meat while cooking. Add carrots, onion and garlic; cook, stirring often, until the carrots and onion soften slightly, about 6 minutes. Add tomato paste and spices; cook, stirring constantly, for 1 minute. Stir the cornstarch mixture and add to the beef mixture along with peas, Worcestershire, pepper and the remaining 1/4 teaspoon salt. Cook, stirring often, until the mixture thickens, 2 to 3 minutes. Remove from heat. Pour meat mixture into casserole dish. Evenly spread the mashed sweet potato mixture over the beef mixture in the skillet. Bake until the topping is hot, 15 to 20 minutes.
