Preheat oven to 350 degrees. Melt chocolate and butter over hot water or in microwave on medium for 4 minutes; remove and stir well. Let cool. Beat the eggs until lemon colored. Gradually add sugar, beating until thick, about 3 minutes. Stir in chocolate. Fold in flour, vanilla, nuts, and chocolate chips. Pour into two greased and floured 8-inch square pans. Bake for 35 to 40 minutes. Do not overbake; they should be very moist in the center. When cool, cut into 2-inch squares. Freezes well.