1. Using 1 3/4- to 2-inch cookie cutter coated with cooking spray, cut Pop-Tarts® into 10 desired shapes. Set aside.
2. In medium saucepan stir together sugar and cornstarch. Stir in peaches, blueberries and nectar. Cook over medium-high heat until boiling and thickened, stirring frequently. Remove from heat. Stir in vanilla. Pour into 8 x 8 x 2-inch baking dish.
3. Place Pop-Tart® shapes, frosting side up, on top of hot filling. Loosely cover with foil. Bake at 350°F for 10 minutes. Remove foil. Bake at 350°F for 5 minutes more. Let stand for 10 minutes. Serve warm with vanilla ice cream, if desired.