Place a large shallow skillet over medium-high heat with the oil. Once hot, add ground beef and cook until no pink is left. Add the sliced hot dogs and cook for another 1 to 2 minutes until brown. Stir in the onion and garlic and cook until softened, another 1 to 2 minutes longer.
Add the tomato paste, worcestershire sauce, spices, salt, pepper and flour, and cook for about 30 seconds to develop their flavors. Stir in the broth, diced tomatoes, pinto beans, tomato sauce and sugar and bring to a simmer. Reduce heat to low and cook, stirring often, until the chili has thickened, about 20 to 25 minutes. Remove from the heat and allow to cool slightly.
Meanwhile, to make the topping, place the potatoes in a large pot and cover with cold water. Set over moderate heat and bring to a boil. Cook until the potatoes are fork tender, about 15 minutes. Drain and return the potatoes to the pot. Add the butter and buttermilk and mash until smooth. Season with the salt, pepper, and garlic.
Meanwhile, preheat oven to 375°F.
Transfer the filling mixture to a casserole dish and top with the mashed potatoes, spreading out to an even layer as best as possible. Bake until the top is golden brown, about 20 to 25 minutes. Remove from the oven and let cool slightly. Top with the cheese, diced onion and scallions right before serving. Enjoy!