Cut up the potatoes into even pieces. The smaller the potatoes the quicker they will cook. Place the potatoes in a pan of cold water and bring to the boil. When the potatoes fall apart when you put a fork through them, they are ready. Drain the potatoes and put them in a bowl. (You can use a standalone mixer to get a creamy and smooth consistency). Add the milk and the butter to the bowl and mix until creamy and smooth.