Preheat oven to 350 degrees F (175 degrees C). In large bowl, mix butter, sugar, eggs and vanilla until light and fluffy. In separate bowl, combine flour, cocoa, baking soda and salt; stir into the butter mixture until well blended. Stir in chocolate chips and walnuts. Drop by rounded teaspoons onto ungreased cookie sheets. Bake 8-10 minutes, until just set. Cool slightly on cookie sheets before transferring to cooling racks to cool completely. Makes about 4 dozen cookies.