Heat oven to 375°F. Bake biscuits as directed on bag.
In medium saucepan, stir together sugar, cocoa and flour. With wire whisk, stir in milk. Cook over medium heat, stirring constantly, until mixture thickens.
Remove from heat; stir in butter and vanilla until melted and smooth.
Split warm biscuits; place on serving plates. Spoon gravy over warm split biscuits.