Preheat oven to 350°F. Spray two 9-inch square baking pans with a cooking spray with flour.
In a large bowl, cream butter and sugar until light and fluffy. Add eggs and vanilla; mix well.
In a separate bowl, combine the flour, cocoa, baking powder, and salt; gradually add to creamed mixture just until blended, being very careful to not overmix.
Pour into both of the prepared baking pans. Sprinkle with semi-sweet and white chocolate chips. Bake at 350° for 30-35 minutes or until a toothpick inserted near the center comes out clean.