In a saucepan, combine Splenda Sugar Blend, corn syrup, milk, and chocolate. Cook over medium heat, stirring constantly, until candy thermometer reaches 232°F, about 6 minutes.
Remove from heat and add butter; do not stir. Set aside to cool to room temperature, about 1 hour.
Transfer mixture to a bowl. Add vanilla and beat on medium speed with an electric mixer until frosting reaches a thick spreadable consistency, about 5 minutes.