1. Lightly grease a 9×13-inch baking dish with butter or non-stick spray.

2. Cut the brioche or challah into 1-inch cubes and place half in the prepared dish.

3. In a bowl, whisk together eggs, eggnog, brown sugar, vanilla extract, cinnamon, nutmeg, and melted butter until smooth.

4. Layer the remaining bread cubes over the first layer, then pour the custard evenly over all the bread, pressing gently.

5. Cover the dish tightly and refrigerate for at least 8 hours or overnight.

6. Preheat the oven to 350F (175C) and let the casserole rest at room temperature for 20 minutes.

7. Bake uncovered for 40–50 minutes until the top is golden and the center is set, tenting with foil if it browns too quickly.

8. Allow to cool for 10 minutes, then dust with powdered sugar and serve with maple syrup if desired.