In a large bowl, cream together the butter, white sugar, and brown sugar until smooth.
Beat in the egg and vanilla. Combine the flour, cocoa, baking soda, and salt; stir into the creamed mixture.
Mix in the chocolate chips. Drop by rounded spoonfuls onto ungreased baking sheets.
Bake for 8 to 10 minutes in the preheated oven, until set. Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.
Interesting Facts
Chocolate chips were invented in 1941 by Ruth Wakefield.
Chocolate chip cookies are the most popular cookies in the United States.
Chocolate chips can be used in many other recipes, including cakes, muffins, and brownies.