Preheat your oven to 160ºC (320ºF) and line a muffin tray with cupcake liners.

In a bowl, combine granulated sugar, cocoa powder, flour, espresso powder, baking powder, baking soda, and salt. Whisk together.

In another bowl, whisk together sour cream, vegetable oil, eggs, vanilla extract, and boiling water until smooth.

Pour the wet ingredients into the dry, using a spatula to combine gently until just mixed.

Spoon the batter into cupcake liners and bake for 20-23 minutes until a toothpick comes out clean. Cool for 5 minutes in the tray before moving to a rack.

Beat together room temperature butter and creamy peanut butter for the frosting until light and fluffy. Gradually add in powdered sugar, vanilla extract, and milk until combined.

Hollow out the center of each cupcake and fill with creamy peanut butter.

Pipe the frosting on top of each cupcake and decorate with chopped peanuts and mini Reese's cups.