1. Heat oven to 350 degrees F. Line an 8-inch square baking pan with nonstick aluminum foil; set aside.
2. Place 1 cup of the chocolate chips and the butter in a large microwavesafe bowl and microwave for 1 minute. Stir until smooth. Microwave an additional 30 seconds, if needed.
3. Whisk in sugar, then eggs. Stir in flour and salt until smooth. Fold in 2/3 cup of the chopped macadamia nuts and the vanilla. Transfer batter to prepared pan.
4. Bake at 350 degrees F. for 25 to 29 minutes.
5. Sprinkle remaining 1 cup chocolate chips over brownie and return to oven for 2 minutes. Remove from oven, and spread melted chips until smooth, to form a frosting. Top with remaining 3 tablespoons nuts. Refrigerate 1 hour to firm chocolate, then cut into squares