COMBINE flour, cocoa, baking soda, and salt in a medium bowl; set aside.
BEAT butter and both sugars on medium-high speed in a large bowl until light and fluffy, about 3 minutes. BEAT in the egg. Gradually ADD the flour mixture on low speed until completely blended. STIR in chopped chocolate.
DIVIDE dough in half. SHAPE each half into a 1 1/2-x 8-inch log. WRAP each log in Reynolds Kitchens Quick Cut Plastic Wrap. REFRIGERATE at least one hour until logs are chilled and firm enough to slice.
PREHEAT oven to 350 degrees F. Line cookie sheets with Reynolds Kitchens Parchment Paper. SLICE cookie logs into 1/4-inch rounds. PLACE rounds 2 inches apart on lined cookie sheets, gently reshaping edges if necessary.
BAKE until edges are set, 13 to 14 minutes. Cool for 2 minutes on a cooling rack. Carefully slide parchment paper with cookies onto a cooling rack; cool cookies completely on parchment paper.
MAKE sandwiches using your favorite pint of ice cream. Using a large knife, CUT directly through the ice cream to make clean slices. Place an ice cream round onto cookie. ROLL edges in coarsely crushed candies to decorate.
PLACE in a single layer in an airtight container lined with Reynolds Kitchens parchment paper. FREEZE immediately until ice cream is firm. Separate layers of cookies with sheets of parchment paper. Keep frozen until ready to serve.