A sweet surprise awaits in the center of this cupcake -- no messy extra steps required, thanks to the genius addition of a store-bought cream-filled chocolate cookie.
Preheat oven to 350 degrees. Line two 12-cup muffin tins with paper liners. In a large bowl, combine flour, cocoa, sugar, baking soda, baking powder and salt. Add eggs, melted butter, buttermilk, vanilla and 1/2 cup hot water; whisk until smooth.
Spoon 1 tablespoon batter into each muffin tin and press a cookie firmly into each cup until batter comes up sides of cookies. Divide remaining batter evenly among cups. Bake, rotating pans halfway through, until cupcakes are puffed and set, 15 to 17 minutes. Let cool completely in pan on wire rack.
Put the buttercream in a large piping bag fitted with a 1/2-inch plain round tip (such as Ateco #808). Pipe onto cupcakes and sprinkle with crushed crumbs.