Preheat oven to 325 degrees F. Line two 9-inch round cake pans with nonstick foil or circles of parchment paper.

In a mixing bowl, using low speed of an electric mixer, beat the butter, shortening and cocoa powder until well mixed. Gradually add both sugars, increasing speed to medium and scraping sides of bowl occasionally. Beat in the vanilla extract and egg. When well mixed, add the salt and baking powder and beat until incorporated.

By hand, gradually stir in the flour, followed by the chocolate chips.

Divide batter in half and spread each half in a lined cake pan for form a circle. Leave a ½ inch gap between the dough and the edge of the pan.

Bake cookies on center rack at 325F for 20 minutes or until set.

Let cool completely in pan. When cool, lift from pan and frost with your favorite frosting.