Preheat oven to 350 degrees. Line 18 muffin cups with paper liners.
In a small bowl stir until smooth the boiling hot water and the cocoa powder. Let cool to room temperature.
In another bowl, whisk together the flour, baking powder, baking soda and salt.
Then in the bowl of your electric mixer beat the butter and sugar until light and fluffy. Add the eggs, one at a time, beating until smooth. Scrape down the sides of the bowl as needed. Beat in the vanilla extract. Add the flour mixture and beat only until incorporated. Then add the cooled cocoa mixture and buttermilk and stir until smooth.
Fill each muffin cup about two-thirds full with batter and place 2-3 peanut butter cups in each cup (DO NOT PUSH THEM IN LET THEM SINK ON THERE OWN). Bake for about 18 - 20 minutes or until risen, springy to the touch, and a toothpick inserted into a cupcake comes out clean. (Do not over bake or the cupcakes will be dry.)
Remove from oven and place on a wire rack to cool.