Preheat oven to 350 degrees F (175 degrees C). Grease a 13x9x2 inch baking pan and set aside.
In a large mixing bowl, combine melted butter, sugar and vanilla. Then beat in eggs one at a time, until well blended.
In a separate bowl, sift or combine flour, cocoa powder and salt. Slowly stir flour mixture into egg mixture until evenly blended. Add chocolate chips (or any other desired additives like nuts). Then spread evenly in greased baking pan.
Bake in preheated oven for 35-40 minutes or until inserted toothpick comes out clean. Remove and cool completely before cutting.