1. Heat oven to 350 degrees F. Line a cookie sheet with a silicone baking mat or parchment paper.
2. Place butter and sugar in the bowl of a mixer fitted with a paddle and beat until smooth and creamy. Add the eggs and vanilla, one at a time, beating well between additions. Scrape down side of bowl. Place flour, cocoa powder, baking soda, baking powder and salt in a separate bowl and mix well. Gradually add to the butter mixture and beat until everything is well incorporated. Scrape down the side of the bowl and beat again. Add nuts.
3. Place heaping teaspoonfuls of dough 2 inches apart on the prepared cookie sheet and transfer to 350 degrees F oven. Bake until the edges begin to firm up, 12 to 14 minutes; do not overbake. For crispy cookies, let cool on cookie sheet. Transfer to a wire rack and repeat with the remaining dough.