1Butter bottom and sides of 9-inch square pan, or line with foil.
2In 2-quart saucepan, heat baking chips, marshmallows and milk over medium heat, stirring constantly, until chips and marshmallows are melted and mixture is smooth.
3Stir in vanilla and pecans. Immediately pour into pan. Cover; refrigerate until firm, about 4 hours. Cut candy into 1-inch squares.