Line an 8x8 inch pan with parchment paper and set it aside.
Add the peanut butter and softened butter to the bowl of a stand mixer fitted with the paddle attachment. Beat until completely combined and smooth.
Next add the vanilla and salt. Mix to combine. Scrape down the sides of the bowl, if needed.
With the mixer on low speed, slowly add the powdered sugar. Mix just until the powdered sugar is incorporated and the dough comes together into large crumbles.
Transfer the peanut butter dough to the prepared pan and press it into a smooth even layer. For a smooth top, place a piece of parchment paper over the bars and then press down to compact them.
Add the chocolate chips and coconut oil to a medium-sized microwave safe bowl. Heat the chocolate for 30 second intervals, stirring between each interval.
Pour the melted chocolate over the peanut butter bars and spread it into an even layer.
While the chocolate is still wet, top it with sprinkles.
Place the buckeye bars in the fridge to set for 20 minutes, or just until the chocolate is no longer wet.
Use a sharp, flat-bladed knife to cut the bars into your desired size. For clean cuts, run the knife under warm water and wipe it clean between each slice.
Enjoy these buckeye bars chilled or at room temperature. Store them in an airtight container in the fridge for up to 5 days.