1. Heat oven to 350 degrees and spray a 9x13 baking pan with cooking spray.
2. In a large mixer bowl, beat all ingredients except chocolate chips together on low speed just until blended. Scrape down the bottom and sides of bowl, then beat for two more minutes at medium speed. At the end of the two minutes, fold in the chocolate chips.
3. Pour batter into the prepared pan, then bake 18 to 20 minutes. Check for doneness with toothpick. (When cake is done, toothpick inserted in center of cake will come out with no crumbs.)
4. Cool completely before icing the cake.
3 cups powdered sugar
2/3 cup cocoa powder
1 stick of butter, softened
1 teaspoon vanilla extract
5 tablespoons milk
In a large mixer bowl, combine one cup of the powdered sugar, the cocoa, the butter, 3 tablespoons milk, and the vanilla extract, beating together until creamy. Gradually beat in the remaining two cups of powdered sugar and milk. If you don't need all the milk, don't use it; check the texture of your icing as you go. If more milk is needed, add up to one extra tablespoon, making a total of six tablespoons of milk.