Chocolate Cupcakes with Oreo Buttercream

  cup  (113g) unsalted butter

  oz  semi-sweet baking chocolate

  large eggs, ( room temperature)

  cup  (150g) granulated sugar

  tsp.  vanilla extract

  cup  (115g) sour cream,  (room temperature)

  cup  (42g) unsweetened cocoa powder

  cup  (95g) all-purpose flour

  tsp.  baking soda

  tsp.  baking powder

  tsp.  salt

or 226g) unsalted butter, (room temperature)

  cups  (500g) confectioners sugar

  Oreo cookies, (finely crushed)

  tablespoons  milk