Combine first 3 ingredients in a large mixing bowl; set aside. Combine sugar and evaporated milk in a buttered Dutch oven. Cook over medium heat, stirring constantly, until mixture reaches soft ball stage or candy thermometer registers 234F degrees; pour over chocolate morsels mixture.
Beat at high speed with an electric mixer or wooden spoon until mixture thickens and begins to lose its gloss. Stir in vanilla and pecans. Spread into a buttered 15 x 10 x 1-inch jellyroll pan. Cover and chill until firm. Store in an airtight container at room temperature.