Place butter in a heavy medium-sized saucepan over medium-low heat and heat until butter boils and bubbles very gently but steadily. Adjust heat as necessary to prevent butter from burning, and continue simmering uncovered for 4 to 5 minutes or until it is golden but not browned, stirring frequently. Be very careful not to burn butter. Immediately remove pan from heat and stir in brown sugar. Pour into a large mixing bowl and refrigerate 50 to 60 minutes, or until mixture resolidifies but is not hard. (To speed chilling, place butter in freezer for about 30 minutes, but don't let it get too hard.)

Preheat the oven to 350 F. Grease several baking sheets and set aside. Grate 3 ounces of the chocolate. Coarsely chop remaining chocolate. Set the two aside separately.

Thoroughly stir together flour, baking powder, baking soda, and salt and set aside. Remove bowl from the refrigerator and beat cooled butter-brown sugar mixture until lightened. Add granulated sugar and beat until fluffy and smooth. Beat in egg and vanilla. Beat in dry ingredients. Add grated chocolate, half of the chopped chocolate, and nuts and stir until well combined.

Roll dough into generous 1 1/2-inch balls. Dip top of each ball into remaining chopped white chocolate, pressing lightly to imbed some pieces in the dough. Space balls, chocolate-studded tops up, about 2 1/4 inches apart on baking sheets. Press down balls just slightly with heel of hand.

Place on center oven rack and bake for 9 to 11 minutes or until just tinged with brown. Reverse baking sheets from front to back halfway through baking to ensure even browning. Be very careful not to overbake. Remove baking sheets from the oven and let stand for 4 or 5 minutes. Using a spatula, transfer cookies to wire racks to cool. Store in an airtight container for 3 to 4 days. Freeze for longer storage.

Unsalted macadamias are preferred for this recipe, but they are hard to find.