Coat 2 (8-ounce) souffle dishes or custard cups with cooking spray. Sprinkle dishes evenly with 1 tablespoon sugar, carefully shaking to coat bottom and sides of each dish; set aside.
Combine milk, flour, and remaining 1 tablespoon sugar in a small saucepan. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Remove from heat. Stir in liqueur.
Beat egg yolk until thick and pale. Gradually stir hot mixture into egg yolk.
Beat egg white, powdered sugar, and cream of tartar in a medium bowl at high speed of an electric mixer until stiff peaks form. Gently fold egg white mixture into milk mixture. Spoon evenly into prepared dishes. Bake at 375° for 15 minutes or until souffles are puffed. Spoon Chocolate Sauce evenly over souffles, and serve immediately.