In a large mixing bowl, combine the chocolate cake mix, thawed whipped topping, and room temperature egg. Beat the mixture at medium speed until all ingredients are thoroughly blended. Cover the bowl and allow it to chill in the refrigerator for 30 minutes.

Preheat your oven to 350°F (175°C). Pour the confectioners' sugar into a shallow dish. Form the chilled dough into balls, using level tablespoons, and roll each ball in the confectioners' sugar until fully coated. Arrange the coated balls on parchment-lined baking sheets, spacing them about two inches apart.

Bake the cookies in the preheated oven until the edges are just set, which should take approximately 11 to 13 minutes. After baking, let the cookies cool on the pans for 5 minutes before transferring them to wire racks to cool completely.