To make the buckeyes, combine the peanut butter, butter, and vanilla extract with a mixer until smooth. Add 1 cup of powdered sugar gradually and mix until firm enough to roll into balls. Shape into 1 tablespoon-sized balls, about 16 in total. Melt the chocolate and dip each peanut butter ball into the chocolate, then place on parchment paper and refrigerate.

Preheat oven to 300°F. In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt. In a separate bowl, whisk together egg, buttermilk, vegetable oil, and vanilla. Combine wet and dry ingredients, then add hot water and mix until smooth. Divide the batter into cupcake liners and bake for about 20 minutes or until a toothpick comes out clean. Cool cupcakes completely.

Prepare the frosting by beating butter, peanut butter, vanilla, and salt until smooth. Gradually add powdered sugar and milk, mixing until desired consistency is reached. Pipe frosting onto cooled cupcakes.

Make the ganache by heating the heavy cream until simmering, then pour over the chocolate chips. Whisk until smooth. Dip the frosted cupcakes into the ganache and top each with a buckeye. Chill before serving.