Step 1: In a large bowl, cream together the softened peanut butter, unsalted butter, and vanilla extract until smooth and well combined.
Step 2: Gradually add the sifted powdered sugar to the peanut butter mixture, mixing until a stiff dough forms. You may need to use your hands to fully incorporate all the sugar.
Step 3: Roll the peanut butter mixture into small, bite-sized balls (about 1-inch in diameter). Place them on a baking sheet lined with parchment paper.
Step 4: Chill the peanut butter balls in the refrigerator for at least 30 minutes, or in the freezer for 15 minutes, until firm.
Step 5: While the balls are chilling, melt the chocolate chips and shortening (or coconut oil) together. Use a double boiler or microwave in 30-second intervals, stirring well after each, until smooth and glossy. Be careful not to overheat the chocolate.
Step 6: Remove the chilled peanut butter balls from the refrigerator. Using a toothpick, spear a peanut butter ball and dip it into the melted chocolate, leaving a small circle of peanut butter exposed at the top. Gently tap off any excess chocolate.
Step 7: Carefully transfer the dipped Buckeye to the parchment-lined baking sheet, using a second toothpick or small spoon to help slide it off the first toothpick. Repeat with the remaining peanut butter balls.
Step 8: Chill the finished Buckeyes for at least 30 minutes, or until the chocolate is fully set. Store in an airtight container in the refrigerator.