Beat butter and sugar until creamy. Add the egg and vanilla and beat until smooth.
In another bowl, stir together the flour, cocoa powder, baking soda and salt. Add slowly to the mixture and beat until well-mixed. Batter with be sticky.
Stir in chocolate chips. Spoon onto cookie sheet.
Bake at 350 for 8-9 minutes. Do not over bake! Cool slightly on the pan and then transfer to wire rack to finish cooling.