Spray a 9-inch square baking dish with cooking spray.
Cut 10 1-inch-thick slices from baguette. Arrange in baking dish.
To make the custard:
In a large bowl, whisk egg whites until frothy. Then whisk in milk, nutmeg, vanilla and 2 tablespoons brown sugar.
Pour evenly over bread, turning slices to coat evenly.
Cover pan. Chill at least 8 hours or overnight, until liquid is absorbed by bread.
To make the French toast:
Preheat oven to 400 degrees F.
Drop blueberries evenly over bread..
In a small bowl, stir together 2 tablespoons brown sugar and oil, and pecans if using. Spoon evenly over bread.
Bake, uncovered, about 20 minutes, until liquid from blueberries is bubbling.