Cumin-and-Chile-Braised Collard Green Stems

In a large skillet, heat the oil. Add the chiles, garlic and cumin; cook over moderate heat, stirring, until fragrant, 1 minute. Add the collard stems and cook, stirring, until bright green, about 3 minutes. Add the stock. Cover and cook over moderately high heat, stirring occasionally, until the stems are tender, 10 minutes. Swirl in the butter, season with salt and serve.