1Heat a generous drizzle of oil in a large, heavy skillet set over medium-high heat. Season the beef with salt and pepper and brown it in batches, setting it aside in a bowl as you go. Add the onion to the pan and cook for a few minutes, until it softens and starts turning golden; add the garlic, jalapeno and ginger and cook for another minute.
2Return the beef to the pan with the curry paste, coconut milk and stock; reduce the heat, cover and simmer for 30 minutes to an hour, until the meat is very tender. Add the sweet potato and cook for another 20 minutes minutes, until it's tender too.
3Stir in the kale and peanut butter, if you're using it, and cook for a few more minutes, until the kale wilts. Add a squeeze of lime and serve over rice, with lime wedges and cilantro, if you like. Serves 4-6.