Buttermilk is the secret to this light and lemony baked French toast recipe. Whisk together the eggs, buttermilk, cream, sugar, and other ingredients. Dip the bread slices individually in the egg mixture, saturating both sides, just like you would for a traditional French toast. This will ensure that the bread is evenly soaked and there are no pockets of eggy custard at the bottom of the dish. After placing the bread slices in the baking dish, let stand an hour before baking. Are you hosting a weekend brunch or have overnight guests coming? Make this satisfying and delicious breakfast casserole ahead of time. Let the bread slices soak, covered, in the baking dish one day before serving. As the oven preheats, allow the casserole dish to come to room temperature. Drizzle this oven baked French toast casserole with powdered sugar or maple syrup and serve with fresh fruit.