Hamburger Casserole

Heat oven to 425 degrees F. Place the potatoes in a medium pot, cover with cold water and bring to a boil. Add 1 teaspoon salt, reduce heat and simmer until just tender, 12 to 15 minutes. Mash with the sour cream, milk, Cheddar and 1/4 teaspoon each salt and pepper. While the potatoes are cooking, heat the oil in a 10" oven-safe skillet. Add the onion and cook, covered, stirring occasionally, for 6 minutes. Add the carrot and cook, covered, stirring occasionally, until just tender, 5 to 6 minutes. Add the beef and cook, breaking it up with a spoon until no longer pink. Add the tomato paste and cinnamon and cook, stirring, for 1 minute. Add the flour, thyme and 1/4 teaspoon salt and 1/2 teaspoon pepper and cook, stirring, for 1 minute. Add the tomatoes and broth and gently simmer until the liquid has nearly evaporated, 4 to 6 minutes. Spoon the potatoes over the beef mixture and use a fork to create ridges in the potatoes (this will make for a crispier topping). Bake until the potatoes are golden brown and slightly crisp, 15 to 20 minutes. Broil, if desired.