Preheat oven to Grease & flour a 9"x13" oblong cake pan.
Cream butter, cream cheese & Splenda together in a large deep bowl. Add melted chocolate & eggs & beat well. Mix baking powder & flour, then add to the creamed mixture. Beat until well blended. Mix in vanilla. Add nuts & chocolate chips & blend well with rubber spatula.
Spoon into baking dish and bake at 350º F for 25 minutes