Preheat oven to 350 degrees. Spray a 9 x 9 baking pan or dish with a non-stick cooking spray. (I used a spray that has flour in it.) Or you can grease and flour the pan. Set aside.
Remove 15 cherries from jar, pat dry, remove stem and cut each cherry into half and cut the halves in half again. (Remember to save juice from jar.) You will need an additional 16 cherries with stems on them for the topping after cake is baked.
Place the cut cherries, dry cake mix and cherry coke into a large mixing bowl. Mix using an electric hand mixer until well combined. (NOTE: you will not be adding any eggs, oil or water listed on back of box cake mix. The cherry coke will be the liquid.)
Pour cake batter into prepared baking pan or dish. Place in preheated oven and bake for 25-30 minutes until toothpick comes out clean in center of cake. Remove from oven and cool completely in pan on a cooking rack.
To make the frosting cream together softened butter, 1/3 cup cherry juice and 3 cups of powdered sugar added 1/2 cup at a time on low speed until a thick consistency is formed.
Spread frosting on cooled cake still in the pan. Using a large long knife, carefully score the frosting into equal 16 squares. (At this time you are not cutting the cake all the way through, just the frosting.) Using a paper towel, dry off reserved 16 cherries with stems on them and place each cherry into each piece of cake pushing into frosting to hold cherry in place.
Grate chocolate over cake a a garnish if desired.
Refrigerate cake for 30 minutes to set the frosting. Cut into servings.