Line 13x9-inch baking pan with foil extending over edges to form handles.
Microwave unsweetened chocolate and butter in large microwavable bowl on HIGH 2 minutes or until butter is melted.
Stir until chocolate is completely melted.
Stir sugar into chocolate until well blended.
Mix in eggs and vanilla. Stir in flour, chopped semi-sweet chocolate, nuts and raisins until well blended. Spread in prepared pan.
Bake at 350°F (325°F for glass baking dish) for 30 to 35 minutes or until toothpick inserted in center comes out with fudgy crumbs.
DO NOT OVER BAKE. Cool in pan.
Lift out of pan onto cutting board.
Cut into squares.