Preheat oven to 375°. In a large bowl, mix flour, cocoa powder, sugar, baking powder, baking soda, and salt. Add in butter and egg. Stir until completely mixed. Fold in white chocolate and nuts. Line baking sheet with parchment paper. Using a tablespoon, drop dough onto cookie sheet, leaving space between each drop. Bake for 8-10 minutes. Allow the macadamia nut cookies to cool on sheet for 2 minutes and then move to cooling rack.