For the Cupcakes:

1. Heat oven to 350°F. Line 24 cupcake tins with paper liners and set aside.
2. In a large mixing bowl, stir together sugar, flour, cocoa, baking powder, baking soda and salt. Add eggs, milk, oil and vanilla; beat for 2 minutes on medium speed. Stir in boiling water. Fill muffin tins 2/3 full.
3. Bake for about 15 minutes, until cupcakes are puffy and spring back when lightly touched in the center. Remove from oven and let cool in pans for 10 minutes. Remove to wire rack to cool completely.

For the Peanut Butter Cup Filling:

1. Combine graham cracker crumbs, peanut butter, butter, and powdered sugar in the bowl of your mixer. Beat on medium speed until smooth and combined.
2. Using a cupcake corer or a small paring knife, remove a circle of cake out of the top center of each cupcake (should be about  1/2" inch – 1" deep).
3. Fill hole with a scoop of peanut butter cup filling.

For the Frosting:

1. In the bowl of your mixer, beat butter, peanut butter, and vanilla on medium speed until smooth.
2. With the mixer on medium low, slowly add powdered sugar until just combined.
3. Add 1/3 cup heavy cream and slowly increase mixer speed to high. Beat at high for one minute. If frosting is too thick, add a bit more cream and beat until smooth.
4. Generously frost or pipe frosting on cupcakes. Chill cupcakes until frosting is cold and firm, a few hours.

For the Chocolate Shell:

1. In a microwave safe bowl, heat chocolate chips and shortening, stopping to stir every 20 seconds until smooth.
2. Dip tops of frosted cupcakes in chocolate shell, allowing excess to drip off.
3. Gently press a mini peanut butter cup into melted chocolate before it sets.