Beat the mashed potatoes and butter in a large mixing bowl until the mixture is completely smooth.

Stir in the vanilla.

Gradually add the confectioner’s sugar, about a cup at a time, mixing well after each addition. Continue adding until the mixture forms a thick, pliable dough that can be rolled out without sticking.

Lay out a large sheet of wax or parchment paper and dust it generously with confectioner’s sugar.

Transfer the dough onto the paper and sprinkle more sugar on top.

Roll the dough into a rectangle about ¼ inch thick.

Spread the peanut butter evenly over the surface of the dough, leaving a small border around the edges.

Starting at one long side, roll the rectangle tightly into a log.

Wrap the log in plastic wrap, tucking in the ends, and chill for 10 minutes to firm.

Once chilled, remove the plastic wrap and place the log on a cutting board. Slice into ¼–½ inch pinwheels and serve.