See's Fudge

3 cups (1 1/2 12-oz. pkgs.) milk chocolate chips
1/2 c. (1 stick) butter
1/2 c. (1 stick) margarine
2 c. miniature marshmallows
1 c. canned evaporated milk
4 1/2 c. sugar
1 tsp. vanilla

Place chocolate chips, butter, margarine, and marshmallows in a large bowl and set aside. Mix milk and sugar in a large saucepan. Bring to a boil for 9 minutes. Pour over first ingredients and beat until very smooth. Add vanilla and beat. If desired, add nuts. Place in a glass 9 x 13 dish. Cool at room temperature.