Beat the confectioners' sugar, peanut butter, melted butter, vanilla and salt with an electric mixer until well combined. Form into 1-inch balls and place on a parchment-lined baking sheet. Freeze until firm, about 20 minutes.
Put the chopped chocolate and shortening in a medium, microwave-safe bowl. Microwave for 2 minutes, stirring every 30 seconds until the mixture is completely melted and smooth.
Stick a toothpick or skewer into the top center of each peanut butter ball. Dip the balls into the melted chocolate, leaving a circle of peanut butter still visible. Allow the excess chocolate to drip off and place on a parchment-lined baking sheet.
Freeze the buckeyes until firm, about 30 minutes. Smooth out the hole left by the toothpick with an offset spatula. Serve at room temperature or well chilled.