Preheat oven to 350 degrees.
Cream your butter, white and brown sugars until well blended. Add the eggs and the vanilla.
When well mixed, add in the dry ingredients; flour, baking powder and salt until well incorporated.
Add in 1 cup white chips, chocolate chunks and 1/2 cup nuts.
Spread mixture evenly into a greased 9x13 pan. Sprinkle with remaining 1/2 cup white chocolate chips.
Bake for 25-30 minutes or until golden brown.
Cool and cut into bars. Makes about 24 brownies.