Wash and peel Potato (4) and cut into quarters. Place in a bowl of water and leave to soak for 20 minutes.
Drain potatoes and place in a large pot. Cover by about 3 inches with cold water. Add a generous sprinkle of salt. Bring to the boil and cook until potatoes are tender when poked with a fork, about 45 minutes.
When potatoes are done, drain in a colander in a sink.
While still hot, mash the potatoes with a potato masher or ricer.
Heat the Milk (3/4 cup) and Salted Butter (6 tablespoon) in a saucepan over a medium heat, until butter is melted.
Sprinkle the Baking Powder (1 teaspoon) over the mashed potatoes.
Pour the hot milk and butter mixture over the mashed potatoes.
Mix until combined.
Season with Salt (to taste) and Ground Black Pepper (to taste).