In a large bowl, mix together the peanut butter, butter, peanut flour, powdered sweetener, vanilla extract, and salt until well combined.
Shape the mixture into small balls, placing them on a parchment-lined tray. You can use a tablespoon to measure for consistency. Insert toothpicks into each peanut butter ball, creating a handle for dipping. Place the tray in the freezer and let the peanut butter balls chill for at least 30 minutes.
In a microwave-safe bowl, melt the sugar-free dark chocolate chips and coconut oil together, stirring until smooth. Alternatively, you can melt them using a double boiler on the stovetop. Take the peanut butter balls out of the freezer. Holding onto the toothpick, dip each ball into the melted chocolate, leaving the top uncovered to resemble a buckeye nut.
Place the dipped buckeyes back on the parchment-lined tray and return them to the freezer for another 30 minutes or until the chocolate is set. Once set, remove the toothpicks and store the buckeyes in the refrigerator.