In a medium bowl whisk the flour, cocoa, baking soda and salt together.

In the bowl of a stand mixer beat the butter and sugar together 3 minutes on medium speed.

Scrape down the sides of the bowl and beat in the eggs and vanilla.

On low speed beat in the flour mixture a little at a time. Beat until well combined.

On the lowest speed (or by hand) beat in the chocolate chips and walnuts.

Cover the bowl with plastic wrap and refrigerate 1 hour.

Preheat the oven to 350°F. Line two baking sheets with silpats or parchment paper.

Scoop up slightly rounded tablespoons of the dough and roll into loose balls placing about 2 inches apart on the cookie sheet.

Bake 8 minutes for soft cookies. (You may have to adjust the cooking time to suit your oven and baking sheet.)

Press a few chocolate chips into the top of each one - if desired.

Cool on the pan for 5 minutes then remove to wire racks and cool completely.

Store in a tightly covered container in a cool, dry place up to 1 week.