With electric mixer, combine mashed potatoes, butter, and 1 cup sugar.

Add in remaining sugar, 1 cup at a time. Start by adding 6 cups of powdered sugar, if the dough is not moldable in your hands and can't be rolled into a ball, continue to add sugar until it is firm.

Stir in vanilla.

Refrigerate filling for 1 hour.

Once chilled, divide dough into two pieces and place one piece on a clean surface that you've generously dusted with powdered sugar. Dust the surface of the dough with additional sugar, and use a rolling pin to roll dough out into a rectangle about 1/4" thick. Make sure that your dough can be rolled at this point, if it's too sticky or falling apart, you may need to add more sugar, re-shape it into a ball, and start over.

Once dough has been rolled into a 1/4" rectangle, spread evenly with peanut butter, leaving a small amount of space peanut butter-free around the perimeter of the dough.

Starting with the longer side of your rectangle, gently but tightly roll into a lot.

Use a knife to slice into pieces about 1/2" thick.

Repeat steps 5-8 with remaining half of dough.

Serve and enjoy.