Preheat oven to 375 degrees.
Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl until well blended. Set aside for later.
Beat butter in a bowl with an electric mixer at medium speed for about one minute until it is light and fluffy.
Add brown sugar and granulated sugar to the butter. Beat for two minutes until fluffy.
Add the vanilla to the mixture. Than add the eggs one at a time until well blended.
Add the flour mixture into the mixer in three parts. Beat on low speed for 30 seconds in between. Once all the flour has been added beat for an additional 30 seconds.
Stir in chocolate chunks (and nuts if you choose).
Drop dough, about a tablespoons worth, 2 inches apart onto a greased cookie sheet. Flatten slightly with back of the spoon.
Bake for exactly 10 minutes and let cool on a wire rack for 5 minutes.