01 - In a large mixing bowl, beat together the creamy peanut butter, softened unsalted butter, vanilla extract, and fine sea salt using a hand mixer or stand mixer until the mixture is smooth and creamy.
02 - Gradually add the powdered sugar to the peanut butter mixture, mixing continuously until a thick, pliable dough forms that holds its shape when rolled.
03 - Scoop out heaping teaspoonfuls of the peanut butter dough and roll between your palms into uniform 1-inch balls. Arrange them on a parchment-lined baking sheet, spacing them about 1 inch apart.
04 - Place the baking sheet in the refrigerator and chill the peanut butter balls for at least 30 minutes, or until they are firm enough to handle without losing their shape during dipping.
05 - In a microwave-safe bowl, combine the chocolate chips with coconut oil or vegetable shortening if using. Microwave in 30-second increments, stirring thoroughly between each interval, until the chocolate is completely melted and smooth.
06 - Insert a toothpick into the top of each chilled peanut butter ball. Dip each ball into the melted chocolate, leaving the top quarter uncovered to resemble the appearance of a buckeye nut. Gently shake off any excess chocolate.
07 - Return each dipped cookie to the parchment-lined baking sheet. Carefully remove the toothpick and use your fingertip to gently smooth over the small hole left behind.
08 - Refrigerate the assembled cookies for about 20 minutes, or until the chocolate coating is fully set and firm to the touch.
09 - Serve the buckeye cookies chilled or allow them to sit at room temperature for 10 to 15 minutes for a softer texture. Store any leftovers in an airtight container in the refrigerator for up to 2 weeks.