Step 1: Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan.

Step 2: In a medium saucepan, melt the butter over low heat. Once melted, remove the saucepan from the heat. Stir in the sugar and cocoa powder until well combined. Beat in the eggs, using a whisk or spoon. Add the vanilla extract and mix until the batter is smooth and shiny.

Step 3: In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the chocolate mixture, stirring until just combined. Gently fold in the macadamia nuts and chocolate chips into the brownie batter.

Step 4: Pour the brownie batter into the prepared baking pan, spreading it evenly. Sprinkle some extra chopped macadamia nuts on top, if desired.

Step 5: Place the baking pan in the oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Be careful not to overbake; you want the brownies to be fudgy and moist.

Step 6: Let the brownies cool in the pan for about 10 minutes. Cut into squares and serve.