Spread blueberries in bottom of 13x9" baking dish and sprinkle with sugar, cinnamon and cornstarch. Set aside.
In a bowl, combine eggs, milk, baking powder and vanilla. Slice bread and dip each slice into mixture. Place dipped bread on top of blueberries, cover and refrigerate overnight.
Preheat oven to 425 degrees. Place pan uncovered, in preheated oven until lightly browned; about 25 minutes. Makes 4 to 6 servings. Enjoy!