Heat the oven to 350 degrees. Line a 9-inch square pan with foil and spray with non-stick cooking spray. In a medium microwave safe bowl, microwave 1/3 cup butter and the chopped unsweetened chocolate on High for 30 seconds and stir.
Microwave for 30 seconds longer; stir until smooth and slightly cooled. If the chocolate isn't completely melted, microwave an additional 10 seconds. Stir in the granulated sugar and brown sugar. Add the eggs, vanilla and 1/3 cup sour cream and beat until smooth. Stir in the cocoa, flour and salt until well blended
Spread in the pan. Bake for 23 to 26 minutes or until the edges are dry and the center is set. Cool completely, about 1 1/2 hours.
In a medium mixing bowl, beat the powdered sugar, ¼ cup sour cream, softened butter, and peppermint extract with electric mixer on low speed until moistened.
Beat on medium speed for 1 to 2 minutes or until creamy and smooth (the mixture will be thick). Spread over the cooled brownies. Refrigerate at least 30 minutes or until the filling is firm. In a small microwave safe bowl, microwave the chocolate chips and warm cream on High for 30 seconds. Stir until smooth and slightly cooled.
Carefully spread over the filling. Sprinkle with the crushed candy. Refrigerate for 30 minutes or until the chocolate and filling are set. Remove from the pan by grasping the edges of the foil and lifting. Peel off the foil. Cut squares, cleaning the knife blade after each cut. Store loosely covered in the refrigerator.