Preheat the oven to 350. Line muffin pans with cupcake liners. This recipe makes 16 cupcakes.
In a medium bowl combine the flour, cocoa, baking soda and salt. Set aside.
In the bowl of a stand mixer mix together the oil and the sugar.
Add the egg, egg yolk and vanilla and beat just until combined.
Add the flour mixture in three parts, alternating with the buttermilk.
Add the hot coffee and mix on low just until incorporated.
Using an ice cream scoop or a spoon fill the cupcake liners about ¾ of the way full. One scoop from an ice cream scoop is the perfect amount.
You will use 16 of the mini peanut butter cups in the batter and the remainder for decoration. With one peanut butter cup per cupcake, roughly chop or quarter it and place it on top of the batter. No need to mix it in, it will sink while baking.
Bake for 18-20 minutes. Move to a cooling rack to cool completely before frosting.
Chocolate Peanut Butter Ganache
Bring the heavy cream to a simmer. Pour over the chocolate chips. Let sit for about a minute to start melting and then whisk until smooth.
Whisk in the peanut butter.
Cover and refrigerate until firm enough to pipe. It should take between 1.5-2 hours to reach a consistency like peanut butter. If you make the ganache in advance and it's too firm, microwave at 5 second intervals until soft enough to pipe or spread.
To frost the cupcakes I am using a piping bag with no tip, I cut about an inch away from the point. You can also use a table knife or offset spatula to spread the ganache on the cupcakes.
Half the remaining peanut butter cups and place one half on each cupcake for decoration.