Combine cubed potatoes and water in a pot over medium heat. Bring to a boil. Add salt and simmer for 15 minutes stirring occasionally. When it is done most of the water would have been absorbed.
Add ground pepper, mustard powder, and milk. Mash with a masher until smooth.
Pour in half of the melted butter and mix it in with a spatula. Transfer to a serving bowl. Drizzle the rest of the melted butter onto the mashed potatoes and garnish with chopped parsley.
Serve immediately with Creamy Turkey Gravy.