Dressing: Put Miracle Whip in a cup or jar. Add mustard, sugar and milk (1 tsp at a time) until it is a desirable, smooth consistency.
Pour dressing on contents of bowl a little at a time. Gently mix through until it lightly coats the potato & egg and is a balance you like. As much or as little as you like will make it perfect for you. I don't like it runny.