Preheat your oven to 350°F (175°C) and generously grease a baking dish with butter.

Cube the stale French bread or challah into 1-inch pieces and place them in a large bowl.

Whisk together the eggnog, eggs, brown sugar, cinnamon, nutmeg, and vanilla extract in another bowl.

Pour the aromatic custard mixture over the bread cubes and gently fold them together until fully soaked. Let this mixture sit for 10 minutes.

Transfer the soaked bread mixture into the greased baking dish, topping with raisins or nuts if desired.

Bake for 45-50 minutes, or until the top is golden brown and set in the middle.