Combine powdered sugar and graham cracker crumbs in a bowl.

In a saucepan, heat butter and peanut butter over low heat until melted and smooth.

Remove the saucepan from the heat.

Stir the crumb mixture into the melted butter and peanut butter until well combined.

Shape the mixture into walnut-sized balls.

Place the balls on a baking sheet lined with parchment paper.

In a small saucepan, heat chocolate chips and shortening over low heat until melted and smooth, stirring constantly.

Roll each peanut butter ball in the melted chocolate to coat completely.

Place the chocolate-covered balls on waxed paper.

Refrigerate for at least 10 minutes, or until the chocolate is set.