Preheat oven to 350 degrees F. Grease an 8x8x2-inch baking pan or line with foil; set aside.
In a small heavy saucepan, combine the 6 ounces white chocolate and the butter. Cook and stir over low heat until melted. Cool for 10 minutes. Add eggs and sugar. Beat with a wooden spoon until combined. Add flour and vanilla; stir just until smooth. Stir in macadamia nuts.
Spread batter in the prepared baking pan. Bake about 25 minutes or until top is lightly browned.
Immediately sprinkle with the 2 ounces white chocolate. Let stand until chocolate is melted; spread over uncut brownies. Cool in pan on a wire rack. Cut into brownies. Makes 16 brownies.