In a microwave, melt chocolate chips and butter; stir until smooth. Cool slightly. In a large bowl, beat eggs and sugar. Stir in vanilla and chocolate mixture. Gradually add flour and mix well. Stir in nuts.
Pour into a greased 13x9-in. baking pan. Bake at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean (do not overbake). Cool on a wire rack. Sprinkle with confectioners' sugar.
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