In a large mixing bowl, combine the peanut butter, butter, vanilla extract, and powdered sugar. Blend until the mixture is a thick, dry dough. If it's not firming up, add more powdered sugar, a little at a time.
Shape the peanut butter into 1 inch rounds, then transfer to a baking sheet lined with parchment paper.
Place a toothpick in each peanut butter ball, the refrigerate until firm, at least 20 minutes.
Meanwhile, melt the chocolate with the vegetable shortening. We recommend either a double boiler or a slow cooker (15-30 minutes on high, keeping any eye on it or 1 hour on low).
Working with a few at a time to ensure they stay cool, dip the peanut butter balls in the chocolate one at a time, leaving a little bit of peanut butter visible at the top. Return to the baking sheet, remove toothpick, and let set at room temperature.
They're delicious served room temperature, or chilled. Store in an airtight container in the refrigerator for 5 days to 1 week.