in a large bowl whisk together eggs, eggnog, sugar, nutmeg, cinnamon, salt, and vanilla
Toss in bread cubes and toss to coat bread completely.
Pour bread and custard into a greased 2.5-quart casserole dish. Spread evenly in the dish. (You could also use a 9-inch x 13-inch baking dish, but the french toast won't be quite as thick.)
Cover the dish and place it in the fridge overnight, or for eight hours.
Preheat the oven to 350 degrees F.
Mix brown sugar and cinnamon in a small bowl.
Uncover french toast and sprinkle top with an even layer of cinnamon brown sugar.
Bake for 45 minutes uncovered. Remove from oven and cut into 8 slices. Serve warm.