Generously season the meat with salt and, if time allows, leave it to sit covered on the bench for 30 minutes.
Heat a large frypan or stovetop casserole over medium-high heat, and when hot, add a splash of oil to the pan. Add about a 1/3 of the meat to the pan and cook until browned, then remove meat from the pan and transfer to a plate. Cook the rest of the meat in batches, adding a little more oil to the pan if needed.
Next, add the onion to the pan and cook for a couple of minutes to soften, then add to the plate of meat.
Scoop 3 tablespoons of coconut milk from the can and add it to the pan, then add the Massaman curry powder and cook on low heat for a minute. Add the rest of the coconut milk, chicken stock, potato and sweet potato, brown sugar, peanut butter and peanuts to the pan and stir to combine. Return the meat and onions to the pan, cover with a lid and simmer for 1.5 to 2 hours (beef or lamb), or until the meat is tender. If using chicken thigh, cook for 45 minutes. If using a slow cooker, allow 4 hours on a high setting or 8 hours on a low setting.
Remove the lid from the pan and simmer for a further 30 minutes or until the sauce thickens to your liking.
Serve with steamed rice, roughly chopped coriander leaves and lime wedges.