1. Heat oven to 400°F. Prepare 2 muffin tins with cupcake liners.
2. Stir together sugar, flour, cocoa, baking powder, baking soda and salt in large bowl. Add eggs, milk, oil and vanilla; beat on medium speed of mixer 2 minutes. Stir in boiling water (batter will be thin).
3. Place one miniature peanut butter cup into the bottom of each well. Pour batter into prepared pans.
4. Bake at 400 for 5 minutes, then reduce the oven temperature to 350 and continue to bake for an additional 25 to 30 minutes, rotating halfway through, until wooden pick inserted in center comes out clean.
Peanut Butter Frosting
1. Prepare a stand mixer with a paddle attachment. Cream your butter and sugar together until smooth. Add in your peanut butter, vanilla, and heavy cream and mix for 8 minutes until very fluffy.
2. Pipe onto each cupcake a swirl of frosting and top with additional miniature peanut butter cups.