1. Butter baking pan, 8 x 8 x 2 inches. Stir milk and chocolate chips in 2-quart casserole; add chocolate. Microwave uncovered on high (100%) 1 minute; stir. Microwave until chocolate is melted and mixture can be stirred smooth, about 2 minutes longer.
2. Stir in vanilla and nuts. Spread mixture evenly in pan. Refrigerate until firm. Cut into 1-inch squares.
