Heat oven to 375°F. Spray 9-inch round cake pan with nonstick cooking spray. In medium bowl, beat margarine and 1/2 cup sugar until well blended. Add vanilla and egg; beat well.
Lightly spoon flour into measuring cup; level off. Add flour, baking soda and milk to margarine mixture; stir just until moistened. Stir in cranberries. Spread batter evenly in sprayed pan.
Bake at 375°F. for 20 to 25 minutes or until toothpick inserted in center comes out clean. Cool slightly.
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.