To make the cupcakes, preheat the oven to 350 degrees F. Line two cupcake pans with paper liners.
In a medium bowl, sift together the flour, cocoa powder, baking powder, baking soda and salt; set aside. In the bowl of an electric mixer, beat the butter on medium speed until smooth. Gradually add the brown sugar and continue beating until fluffy, scraping down the sides of the bowl as needed. Beat in the vanilla. Add the eggs one at a time, beating well after each addition.
With the mixer on low speed, add the flour mixture in three additions, alternating with the buttermilk, beginning and ending with the flour mixture. Mix just until all the dry ingredients have been incorporated, being careful not to overmix.
Divide the batter between the prepared cupcake liners. Bake until a toothpick inserted in the center comes out clean, about 18-20 minutes. Transfer the cupcakes to a wire rack and let cool to room temperature.
To prepare the frosting, in the clean bowl of an electric mixer fitted with the whisk attachment, combine the whipping cream, powdered sugar, and vanilla extract. Beat on medium-high speed until the whipped cream holds stiff peaks. Gently fold in the cookie crumbs with a spatula.
Scoop the mixture into a pastry bag and pipe frosting decoratively on top of the cupcakes. Garnish with Oreo cookie halves.