1. Combine first 5 ingredients in a small saucepan. Cook over medium heat 5 minutes or until sauce comes to a boil and thickens, stirring constantly with a whisk. Remove from heat; whisk in yogurt and vanilla. Pour mixture into a bowl; cool slightly.
2. Place 1 cake slice on each of 4 plates. Serve with 1 cup fruit and about 1/4 cup sauce.