In a saucepan, whisk together Splenda Sugar Blend and flour. Gradually whisk in milk until smooth. Add chocolate.
Cook over medium-high heat, whisking constantly, until mixture comes to a boil; reduce heat and cook over low heat until mixture thickens to a pudding-like consistency, about 5 minutes.
Remove from heat and whisk in butter.
Place saucepan in a bowl of ice water. Let stand, whisking occasionally, until mixture cools and thickens (about 20 minutes). Whisk in vanilla extract.
