Combine the potatoes, milk, vanilla extract, and salt in a large bowl. Mix to combined.

Start adding in the powdered sugar, 1 cup at a time. Once you have added about 4 cups, start adding a little at a time. It will all come together into a dough. It will be hard to stir, so once it gets too hard to stir, pour it out onto a counter and knead, adding more powdered sugar as needed.

Once you have a stiff dough, transfer to a piece of parchment paper that has been sprinkled generously with powdered sugar. Roll the dough out with a rolling pin into a large rectangle, about 12 inches by 16 inches.

Spread the peanut butter evenly over the dough.

Roll the dough up jelly roll style, using the parchment paper to help roll the dough tightly.

Once the dough is rolled into a cylinder, I like to take it and stretch it to about 24 inches long to make it a little bit skinner.

Wrap the roll in plastic wrap. (It is usually easier to cut the roll in half then wrap the two sections separately.) Refrigerate for at least an hour, or overnight.

Once completely chilled, remove the plastic wrap and cut into pinwheels. You should get about 40 pieces, depending on how thick you cut them.