How to Make It
Preheat the broiler. Broil the chiles for about 5 minutes per side, or until the skin is blistered. Transfer to a bowl, cover with a towel and let cool slightly. Lower the oven temperature to 400°.
Heat the oil in a large skillet. Add the onion and cook over moderately high heat until softened, about 5 minutes. Stir in the oregano, salt and cumin. Add the chorizo, black beans, tomato paste and water, reduce the heat to low and cook until warmed through, about 10 minutes.
Peel the chiles, slit them lengthwise and scrape out the seeds. Stuff the chiles with the black bean filling and arrange them in a large baking dish. Bake for 5 to 7 minutes, or until heated through. Transfer to plates, spoon the crème fraîche on top and serve.