Portillo's Chocolate Cake with Chocolate Frosting

Ingredients:
1 box Duncan Heinz Devil's Food cake (word on the street Portillo's uses Betty Crocker but I'm a Duncan Heinz girl. Use whichever you'd like.)
3 eggs
1 cup cold water
1 cup Hellmann's mayonnaise
Chocolate frosting

Directions:
1. Preheat oven to 350 degrees. Grease 2 - 9 inch cake pans.
2. Mix together cake mix, eggs, water, and mayonnaise. Beat for about 4 minutes.
3. Pour into prepared cake pans. Bake for 30 minutes or according to cake directions.

Frosting:
Ingredients:
2 cups butter (no substitutes), softened
9 cups confectioners' sugar
2 1/2 cups baking cocoa
1 teaspoon vanilla extract
1 cup milk

Directions :
In a large mixing bowl, cream butter. Gradually beat in confectioners' sugar, cocoa and vanilla. Add enough milk until frosting reaches spreading consistency. Allow layers to cool on baking rack. Once cooled, transfer to cake platter and frost.