Meanwhile in a large saucepan, place potatoes in enough water to cover. Over high heat, bring to a boil and cook for 15 minutes or until tender; drain well. Return potatoes to the pot and add remaining 4 tbsp butter, remaining ¼ tsp black pepper and the milk. Beat with an electric mixer until smooth and creamy.
Spoon or pipe the mashed potatoes over the meat mixture. Bake for about 20 minutes or until the mashed potatoes are golden and the meat mixture is piping hot.