Preheat the oven to 325° F and line a cookie sheet with a silicone baking mat or parchment paper.
In a large bowl, combine the cake mix, whipped topping, and egg. Stir until combined. The batter/dough will be very sticky.
Pour the powdered sugar into a small bowl. Scoop 1 heaping tablespoon of batter into the powdered sugar. A cookie scoop is very helpful with this. Roll the batter to coat with the powdered sugar. Place the sugar coated batter onto a cookie sheet about 2 to 3 inches part. Continue until the sheet is full. Bake for 12 to 14 minutes or until set. Remove from the oven and allow to cool for about 5 minutes on the pan. Place a chocolate heart in the center of each cookie, if desired. Cool completely on the baking mat or parchment, then use a spatula to remove the cookies. Repeat until all the batter has been used. Store in an airtight container.