1/2 c. (1 stick) unsalted butter
8 oz. white chocolate chips or coarsely chopped white chocolate
2 lg. eggs
Pinch of salt
1/2 c. sugar
1/2 tsp. vanilla
1/2 tsp. salt
1 c. all-purpose flour
8 oz. semi-sweet chocolate chips

Preheat oven to 350 degrees. Lightly butter 8 inch square pan. Line bottom with foil or parchment. Lightly butter foil. Melt 1/2 cup butter in heavy small saucepan over low heat. Remove pan from heat. Add 1/2 of white chocolate, do not stir.

Using electric mixer, beat eggs with pinch of salt in large bowl until frothy. Gradually add sugar and beat until pale yellow and slowly dissolving ribbon forms when beaters are lifted. Add butter, white chocolate mixture, vanilla and 1/2 teaspoon salt, then flour and mix until just combined. Stir in semi-sweet chocolate chips and remaining white chocolate chips. Spoon mixture into prepared pan, smooth top with spatula. Bake until tester inserted in center comes out almost clean. Sift powdered sugar on top.