Toast walnut halves in a frying pan with a knob of butter for 2 minutes.
Cool toasted walnuts and pulse in a food processor until finely chopped.
Mash Stilton, softened butter, port, and peppercorns together in a bowl.
Chill the cheese mixture in the fridge for at least three hours.
Stir the parsley into the chopped nuts in a small bowl.
Roll teaspoonfuls of cheese mixture into balls and coat evenly in the nut mixture.
Place balls on a lined tray and chill until ready to serve.
Serve the balls on a plate with cocktail sticks inserted.