Preheat oven to 375 degrees. Line a 9 by 12 inch baking dish with parchment paper – it is easier to do if you crumple the paper first.

Place the chocolate chips and butter into the bowl of a food processor and pulse a few times to roughly combine. Add the eggs, coconut palm sugar, cocoa powder, corn or tapioca starch, salt, espresso powder and vanilla, and blitz until combined. The batter will be lumpy. Spread the mixture into the prepared baking dish. Sprinkle the chopped nuts over the top and gently press into the batter. Bake for 20 minutes or until the batter is set and feels slightly firm to the touch. The outer edges will appear drier than the inside. Let cool and then cut into 1½ inch squares.