Preheat oven to 350 degrees F and line 3 baking sheets with parchment paper (optional).

With an electric mixer, cream together butter and sugar until smooth. Add vanilla and eggs and beat until combined.

Add flour, baking soda, cocoa, and salt and beat until a dough forms (it should hold together easily but be dry enough that you can roll into balls without coating your hands). Stir in chocolate chips.

Roll dough into 1" balls and place in 4 rows of 3 on prepared baking sheets (you can make larger cookies, but you'll need to be fewer to a pan and bake a little longer). Bake for 8-9 minutes until centers are just set or only a tiny bit glossy in the center -- they will set as they cool.