Take berries out of the freezer and defrost for at least 30 minutes.
Spray a 9" × 13" casserole dish with organic nonstick cooking spray.
Tear bread into pieces and spread them throughout the casserole dish in an even layer.
In a large bowl, mix eggs, egg whites, Greek yogurt, milk, and maple syrup. Mix very well until smooth and thoroughly combined. Pour egg mixture completely over bread.
In a small bowl, mix butter, brown sugar, cinnamon, flour, and pecans, if using. Mix until all ingredients are combined, even if still lumpy.
Add defrosted berries on top of bread mixture.
Sprinkle the butter mixture on top of the bread. Cover and refrigerate overnight. If cooking the same day, make sure to refrigerate at least 30 minutes before baking.
6. In the morning, preheat the oven to 350°F. Bake for 45 minutes until golden brown and the middle of the dish is set. Serve immediately with maple syrup, if desired.
Notes
If you are making this the night before, make sure you cover it toughly with aluminum foil to prevent it from drying out.You can also use the same amount of fresh berries in this casserole.Make sure the butter is cold, it yields a crisper, less soggy casserole.