Add mashed potatoes to a bowl.
Combine mashed potatoes with vanilla and milk.
Mix well.
Shape the dough into a rectangle or square.
Sprinkle powdered sugar onto a clean surface.
Place the dough onto the powdered sugar and roll it out to a ¼-inch thickness.
Spread peanut butter evenly over the rolled-out dough.
Roll up the dough, jelly roll style, starting at the shorter end.
Wrap the roll tightly in plastic wrap and refrigerate for at least 2 hours.
Remove the roll from the refrigerator and unwrap.
Slice the roll into rounds and serve.
