This recipe is adapted from Baking Bites, but I made some changes to the type of bread and amount of streusel. This casserole is so good as it is that you really don't even need syrup!
12 1-inch slices day-old french bread (approx)
2 cups milk (can use soy milk -- I like using vanilla almond milk)
4 large eggs (can use egg whites)
1/4 cup brown sugar
1/4 tsp salt
1 tsp vanilla extract
3/4 tsp ground cinnamon
1/2 cup brown sugar
6 tbsp all purpose flour
1/2 tsp salt
4 tbsp butter, melted
Arrange 1/2 the bread bread in a lightly greased large oval casserole dish.
In a small bowl, make the streusel. Stir together brown sugar, flour and salt. Pour in butter and stir with a form until mixture has the consistency of wet sand. Pour ~1/4-1/3 of the streusel over the bread. Place remaining bread evenly over first layer.
In a large bowl, whisk together milk, eggs, brown sugar, salt, vanilla and cinnamon until smooth. Pour over bread. Press down to ensure all pieces are thoroughly soaked. Custard should just come near the top of the bread layer (although the last time I made it it was only about halfway up and it still tasted good). It if covers it more deeply, add additional bread.
Sprinkle remaining streusel evenly over bread and custard. Cover with plastic wrap and refrigerate overnight. Preheat oven to 350F and bake for about 30-35 minutes, until french toast is a golden brown on top. Let the dish stand for a few minutes. The dish will be very soft and souffle-like, but should not be too runny. The french toast will continue to set and soak up the custard as it cools. Slice and serve warm, with maple syrup if desired.
Not that this recipe is all that "healthy", but for a totally decadent version of this, check out Paula Deen's take on a similar french toast casserole.