Place the haggis in the base of an ovenproof dish. Reheat and refresh the neeps and tatties, in separate saucepans, over a medium heat adding a splash or two of milk. Spoon the neeps over the haggis and smooth the top with a spoon. With a clean spoon, spread the tatties on top, using a fork to decorate if desired. Dot the butter over the tatties, sprinkle with chives and season with salt and pepper.
Bake in the preheated oven on the top shelf for 20 to 30 minutes, until the haggis is piping hot and the tatties are golden brown. Remove from the heat and serve.