How to Make It
Preheat the broiler. Place the chiles and the tomato on a baking sheet and broil, turning occasionally, until blistered and charred all over. Transfer to a paper bag and set aside to steam for 10 minutes. Using a small knife, scrape off the blackened skins. Discard the stems, seeds and ribs and finely chop the chiles. Seed and finely chop the tomato.
In a large bowl, combine the masa harina with 1/4 cup of warm water. Add the ground meat, one-third of the minced garlic, 1/2 teaspoon salt and a generous grinding of black pepper. Mix well with your hands and shape into forty 1-inch balls.
In a medium nonreactive skillet, melt 2 tablespoons of the lard. Add the whole garlic clove and cook over moderately high heat for 20 to 30 seconds, pressing it with the back of a spoon. Discard the garlic and remove the pan from the heat. Whisk the flour into the lard and cook over moderate heat, stirring, until golden, about 1 minute.
Bring the chicken stock to a simmer in a large saucepan. Gradually whisk about 1/2 cup of the stock into the flour mixture, then whisk it into the simmering stock to smoothly combine. Simmer the soup over moderately low heat until very slightly thickened, about 5 minutes.
Heat the remaining 2 tablespoons lard in the skillet over moderately high heat. Add the scallions, roasted chiles and tomato (or tomato puree if using) and the remaining minced garlic. Reduce the heat to moderate and cook until the scallions and garlic are slightly softened, about 2 minutes. Stir into the stock along with the cilantro and mint and simmer for 5 minutes. Add the meatballs and simmer over low heat for 15 minutes. Season with salt and black pepper. Serve warm.