Set a large, heavy skillet over medium-high heat and add a drizzle of oil.
Sprinkle the beef with salt and brown on all sides, then transfer to a plate.
Add the onions to the pan and cook for 3-4 minutes, until soft and golden; add the jalapeño, garlic, ginger and curry paste and cook for another minute.
Return the beef to the pan, add the coconut milk and peanut butter and bring to a simmer; cook for 15-20 minutes, until the sauce has thickened and the meat is tender. Add a splash of water if it’s getting too thick.