Preheat oven to 350 F. Spread macadamia nuts on a cookie sheet and toast them for about 5 minutes in the oven just until they turn golden. Remove nuts from the oven into a small bowl while they are still hot and toss with ¼ teaspoon salt. Then spread them on a plate to cool. Tossing nuts while they are still hot with salt helps salt adhere to nuts.
Make sure butter is not over-melted: it should sit out at room temperature for about an hour and should not be liquid. In a large bowl, using mixer, blend butter with brown sugar until creamy. Add vanilla and an egg and continue beating until creamy again. Add baking powder and flour and beat on low speed for a minute, than on average speed for a couple of minutes until all dry ingredients are well incorporated.
Using spatula, fold macadamia nuts and white chocolate chips into cookie dough.
Place spoonfuls of cookie dough onto un-greased cookie sheet. Bake for about 15 minutes at 350 F. Mid-time through baking, I like to pull the cookie sheet out and flatten the cookies with the butter knife: because the dough is made with colder butter, the cookies don’t spread out as much, and flattening them out just a bit helps their appearance. Don’t flatten them out too much, though. Remove from oven and let cookies cool.