In a bowl, blend the mashed potatoes and vanilla. Using a wooden spoon, gradually add the icing sugar to form a soft dough that also holds together well.
Sprinkle a work surface with icing sugar. Knead the dough for a few minutes until it has the texture of pie dough. On parchment paper, roll out the dough into a 14 x 8-inch (35 x 20 cm) rectangle.
Heat the peanut butter in the microwave for a few seconds and spread over the dough. Holding the paper, roll the dough into a cylinder about 14-inches (35 cm) long. Slide onto a baking sheet and refrigerate for 1 hour. Remove the parchment paper. On a work surface, cut into twenty 1/2-inch (1 cm) slices.
Store in an airtight container.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.