Meanwhile, in small saucepan, combine all sauce ingredients except yogurt; mix well. Bring to a boil over medium-high heat. Boil 8 minutes without stirring. Place yogurt in small bowl; with wire whisk, beat in 1/4 cup hot mixture until well blended. Add yogurt mixture to hot mixture in saucepan, stirring constantly with wire whisk. Serve warm sauce over cake squares.