Grease one 9-inch square baking pan. Line the bottom of the pan with parchment
paper and set aside.
Chop 1/2 of the white chocolate into very small pieces.
Chop the remaining white chocolate and the bittersweet chocolate into large chunks,
Sift together the flour, baking powder and salt.
Melt the butter in a small saucepan. Do not allow the butter to bubble or to
Remove from the heat and add the finely chopped white chocolate. Do not stir
the chocolate in, set aside.
Beat the sugar, eggs and vanilla together until thick and lemon colored, about
Lower the mixer speed and add the butter mixture. Mix just to blend.
Add the flour mixture and mix just until the flour is mixed in.
Use a rubber spatula to fold in the two chocolates and the nuts.
Scrape the batter into the prepared pan.
Bake at 325 degrees F until the brownies are just set, about 30 minutes. A wooden
pick inserted in the center should come out with moist crumbs still attached. As
with all brownies it is better to under-bake than to over-bake.
Allow to cool for about 1 hour then cut into squares.