Preheat the oven to 350 degrees F. In a large bowl, sift together the granulated sugar, flour, cocoa, baking powder, baking soda, and salt. In a separate bowl, beat together the eggs, oil, buttermilk, and vanilla. Mix the wet ingredients into the dry ingredients. Whisk in the hot coffee just until incorporated. Set aside.

In a separate bowl, mix together the peanut butter and confectioners’ sugar until smooth. Roll into twelve balls 1-1/2 – 2 inches in diameter. Scoop about 3-1/2 tablespoons of cupcake batter into the bottom of each of twelve 8-ounce jars. Place a peanut butter ball in the center of each jar and cover with an additional 2 to 3 tablespoons of batter. Wipe up any batter from the outside of the jar or around its rim.

Place the jars 2 inches apart on a large baking sheet. Bake the cupcakes for 18 to 20 minutes, until the tops spring back when touched. Remove from the oven, immediately place of of the chocolate pieces on top of each hot cupcake, and allow the chocolate to melt. Using hot pads, carefully tilt each jar so that the melted chocolate covers the surface of the cake. Let the cakes cool, and serve and room temperature.

Makes 12 individual cupcakes