Preheat oven to the temperature that is listed on the cake mix. Grease 3 9-inch round pans with shortening and then coat them with a light coating of flour.
In a large mixing bowl, add both boxes of cake mix. Add the softened butter, replacing the oil (using the same measurements for butter that is called for oil). Add in the eggs and mix well. Replace the water with the same measurement of hot coffee, adding in slowing, and the peppermint extract and mixing well.
Pour the batter evenly into the 3 prepared pans. Bake for the required amount listed on the cake mix box (about 20-25 minutes).
The cakes are done when you touch the center of the cake and it springs back. Be careful not to open the oven until you think the cakes are done or they may fall in the center.
Allow the cakes to cool for 10 minutes, then turn them onto a wire rack to cool completely.
To Make the Frosting
In a stand mixer bowl, with the mixer on medium speed, whip the butter for 2 minutes until it is almost white in color. Add in the powdered sugar, peppermint and 3 tablespoons milk. Beat on low speed for 3-5 minutes, adding in the last tablespoon of milk if the buttercream needs to be thinner. Add in green food coloring and mix well until you achieve the desired color.
To Decorate the Cake
Place the oreos into a plastic bag and crush either with your hands or with a rolling pin.
Place one cake layer onto a cake plate. Frost with buttercream and sprinkle with crushed oreos.
Place down another cake layer, frost with buttercream and sprinkle with crushed oreos.
Place the final cake on top.
Frost the top and sides of the cake with the remaining frosting.Then decorate the sides of your cake with more mint oreos. Use the remaining icing to pipe along the top for an added decorative touch!
Adjust the amount of mint flavoring in the frosting to your liking.The calories shown are based on the cake being cut into 15 pieces and using all the frosting and cookies. 1 serving is 1 slice of frosted cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. To lower the calories, cut the pieces smaller or use less frosting.