Place the nutmeg, curry powder, soy sauce, chilli and salt and freshly ground black pepper into a bowl and mix well. Add the chunks of beef and mix well to coat evenly in the mixture.
Heat the vegetable oil in a pan until smoking, then fry the meat for 1-2 minutes on all sides, or until golden-brown all over. Remove the beef from the pan and set aside.
Add the onion, pepper and garlic to the pan and fry for for 3-4 minutes, or until softened, then stir in the tomato purée and chopped tomatoes and cook for 2-3 more minutes.
Add the meat back into the pan along with the potato chunks, rum and stock, then bring to boil. Reduce to a simmer and cook for 1 hour to 1 hour 30 minutes, or until the beef is tender.
Stir in the mangoes and thyme and cook for a further 4-5 minutes to heat through.
Serve the Jamaican stew alongside cooked long grain rice, and a rum cocktail if desired.