Preheat oven to 350 F. Line two baking trays with baking or parchment paper.
In a large mixing bowl, using mixer beat cold, cubed butter and sugar together until combined and creamy.
Add egg and mix until just combined.
Add cocoa powder and mix into wet mixture until combined.
Add flour, baking soda and salt and beat on a low speed until soft cookie dough forms.
Add the chocolate chips and macadamia nuts and beat until just combined, taking care not to overmix the batter.
Scoop out cookie dough, roughly 2 tablespoons per cookie (medium cookie scoop), and place on prepared oven trays, leaving room for the cookies to spread some. For larger cookies, use a large cookie scoop.
Bake cookies for 12-14 minutes for medium sized cookies and 14-16 minutes for larger sized cookies. Leave cookies to cool completely. Cookies will firm up as they cool.