Preheat the oven to 350 degrees. In a mixing bowl, blend the butter until smooth and fluffy on medium speed. When the butter is ready, it will turn a light, white color. Add the sugar. Continue to mix until the sugar/butter mixture is smooth. Add the vanilla and eggs and continue to mix. Add the cocoa powder, baking soda, salt and then flour. Mix just until combined. Add the chocolate chips to the batter and mix.
Onto a cookie sheet lined with parchment paper, spoon golf ball sized dough balls onto the sheet. Put 12 cookies on each cookie sheet. Bake for 6-8 minutes, or until the tops of the cookies begin to crack. Remove from the oven and cool on a cooling rack. Serve warm or wait until they cool.