Chocolate cake

This cake I made for one of my friend's surprise birthday party. This was not a planned recipe, I just experimented with the ingredients at home and to my surprise it came out very moist and a hit among the kids as well as adults. So before I forget what I did, I decided to pen it down!
Here are are ingredients

For Cake

• One box of white cake mix
• 3 whole eggs
• 1 and 1/4th cup of water
• 1/3 cup of canola oil
• 1/4th cup of unsweetened cocoa powder
• 1/4th cup of sweet cocoa powder
• 1 teaspoon of coffee extract
• 1/2 tablespoon of instant coffee

For Icing

• 1 teaspoon of coffee extract
• 2 cups heavy of whipping cream
• 1 teaspoon of vanilla extract
• 1/4th cup of sweet cocoa powder
• Icing sugar according to the level of sweetness you want

For Decoration

• Chocolate melts
• 1 tbsp of sweet cocoa powder

Mix all the cake ingredients together and beat it with an electric mixer until the batter is smooth. Pour it equally into three 9-inch baking pans and bake for 20 minutes at 325°F. Take these out of the oven and keep them on a cooling rack for 1-2 hours.

For icing put all the ingredients into a bowl and using an electric mixer (set on medium-high speed) beat it until the mixture is stiff and frosting consistency.
To assemble the cake: Place one cake layer on a serving plate, spread one fourth of the frosting on this layer. Put the next layer of the cake and top it with frosting again, put the final cake layer on and cover the whole cake with rest of the frosting. I try to smooth it out as much as possible.

For decoration 
Sprinkle the sweet cocoa powder on the cake using a sieve and placed chocolate melts on the circumference.

And leave it in fridge overnight to set.