yield: 12 servings  
Minimal prep work and unbelievable taste! Let the refrigerator do all the work and wake up to sweet
blueberry french toast casserole in the morning.  (From http://sallysbaking addiction.com)
1 (12-14 ounce) loaf french bread, sourdough bread, or challah
1 cup fresh or frozen blueberries
8 large eggs
2-1/4 cups  whole milk
1/2 teaspoon  cinnamon
3/4 cup  packed light brown sugar
1 Tablespoon vanilla extract

1/3 cup packed light brown sugar
1/3 cup all-purpose flour
1/2 teaspoon cinnamon
6 Tablespoons unsalted butter, cold and cubed
Optional: extra blueberries, fresh fruit, maple syrup, and/or confectioners' sugar for topping

1. Grease a 9x13 pan with butter or spray with nonstick spray. Slice then cut the bread into cubes, about 1 inch in size. Spread cubes into the prepared baking pan and top evenly with blueberries. Set aside.
2. Whisk the eggs, milk, cinnamon, brown sugar, and vanilla together until no brown sugar lumps remain. Pour over the bread. Cover the pan tightly with plastic wrap and stick in the refrigerator for 3 hours overnight.  Overnight is best.
3. Preheat oven to 350°F. Remove pan from the refrigerator.
4. Prepare the topping: Whisk the brown sugar, flour, and cinnamon together in a medium bowl. Cut in the cubed butter with a pastry blender or two forks. Sprinkle the topping over the soaked bread.
5. Bake for 45-55 minutes or until golden brown on top.  Serve immediately.
Cover leftovers tightly and store in the refrigerator for 2-3 days.
6. Make ahead tip: Prepare the topping in advance, cover tightly, and store in the refrigerator. Sprinkle over the soaked bread before baking. For freezing, prepare the recipe through step 4 (without preheating the oven) and freeze for up to 2 months. Thaw overnight in the refrigerator then bake as directed.