Grease a 13x9" baking pan with cooking spray. Place the cubed bread evenly into the dish.
In a large bowl, whisk together the eggs, eggnog, milk, orange zest and cinnamon until well incorporated. Pour the eggnog mixture over the bread, then press the bread down into the liquid. Cover the dish with plastic wrap and refrigerate overnight.
In the morning, preheat the oven to 350 degrees. Remove the French toast from the refrigerator and remove the plastic wrap.
Bake in the middle rack of your oven for 50 minutes to one hour, or until golden brown and puffed in the center. If the French toast browns to quickly, cover it with foil while it continues to bake.
Cool on a wire rack 10-15 minutes before serving.
Notes
Total time above includes 8 hours for the French toast to soak overnight.
Challah bread may be substituted with a loaf of French bread. Stale or day old bread works even better than fresh.
Lighten up this recipe by using light eggnog or use half whole eggs and half egg whites.
Leftover eggnog french toast casserole keeps in the refrigerator covered with plastic wrap for up to 3 days.
Top your baked french toast with whipped cream or maple syrup if desired. Nutrition information does not include the optional toppings.