In a large mixing bowl, combine the butter, peanut butter, and powdered sugar. It may take some time to come together, but just keep mixing until the ingredients are mostly homogeneous, and then turn it out onto a smooth surface and knead by hand until smooth. It should be clay or playdough consistency.
Shape the dough into 1-1.5 inch balls and place onto a baking sheet lined with parchment paper. Refrigerate the balls for at least 30 minutes.
While the balls are chilling, melt the chocolate. Place the chocolate (if doing both semi-sweet and white chocolate, do this process once with each chocolate) in a microwave-safe bowl along with 1 tbsp vegetable shortening and microwave for 30 seconds at a time, stirring well in between until fully melted. You can also use a double boiler, which I have detailed here. Remove the balls from the fridge. Using a toothpick, pick up a ball and dip it into the melted chocolate. If you wish to add sprinkles, I had a lot of difficulty rolling the balls in the sprinkles, so I would instead recommend you sprinkle them on by hand while the chocolate is still melted.
Place the dipped buckeyes back on the parchment. You can easily smooth over the toothpick hole with your finger, and then place the pan back in the fridge to set for at least 30 minutes. They are good for up to 7 days at room temp, covered.
Enjoy!
