In a heavy bottomed skillet over medium heat, heat the lard until it is shimmering but not yet smoking. Sauté the onion until it has softened and become translucent, about 4 minutes. Add the garlic and stir until it is nice and fragrant, about 1 minute. Add the flour. Stir gently but constantly until the roux reaches a medium brown ("peanut butter") color, about 2 minutes. Add the chile powder or chiles, garlic, chicken broth, oregano, salt and cumin (if using). Simmer, stirring constantly until the sauce has thickened. The sauce should coat the back of a spoon. Add a little water if needed for proper consistency. Blend or process if desired for a smoother texture.