Mix together the mashed potatoes, 1 cup of powdered sugar, the salt and the vanilla.
Slowly add the powdered sugar, 1 cup at a time, mixing between each addition until the mixture forms a dough, slightly thicker than a cookie dough.
Lightly sprinkle your surface with powdered sugar, and roll out the dough into a rectangle shape about ¼" thick.
Spread the peanut butter in a thin layer all over the dough, leaving about a ½" space around the edges.
Roll the dough up lengthwise, and wrap tightly in plastic or wax paper. Chill for about 1 hour, then cut into ¼" to ½" slices.
Notes
*You can use instant mashed potatoes for this, and ½ cup would be about 1 Russet potato.**You can use any nut or seed butter you like or even swap it for nutella or cookie butterCalories are automatically generated. For best results calculate based on your exact ingredients.