How to Make It
Preheat oven to 350°F. Grease and flour a 13- x 9-inch baking pan.
Beat cake mix, water, oil, and egg whites with an electric mixer on medium-low speed until combined and smooth, about 4 minutes. Pour mixture into prepared pan. Bake until a toothpick inserted in center comes out clean, 15 to 20 minutes. Cool cake in pan 10 minutes; invert onto a wire rack and let cool completely, about 30 minutes. Cut cake in half.
Stir together powdered sugar, butter, and 1 teaspoon of the milk in a medium bowl until mixture is smooth and creamy, stirring in up to 1 teaspoon more milk, if necessary.
Crumble 1 cake half into bowl with powdered sugar mixture and stir until well combined.(Reserve remaining cake half for another use) Using your hands, shape tablespoonfuls of cake mixture into 20 balls. Press 1 cherry into each cake ball, pressing cake around cherry to completely cover and leaving stem exposed. Roll balls between palms to smooth cake coating, and place on parchment paper-lined baking sheets.
Melt chocolate coating according to package directions. Dip cake-covered cherries in chocolate coating, covering completely and scraping off excess on side of bowl; return to baking sheet and set aside until chocolate sets, about 15 minutes. Layer between sheets of wax paper in an airtight container, and store in refrigerator for up to 5 days. Let stand at room temperature 20 minutes before serving.
Note: You may use 2 (8-inch) square pans instead of 1 (13- x 9-inch) pan.