Grease a 9x13-inch baking dish with the melted butter to prevent sticking and add flavor.
Arrange the cubed brioche bread in an even layer inside the prepared baking dish.
In a large mixing bowl, whisk together the eggs, non-alcoholic eggnog, whole milk, 1/4 cup sugar, vanilla extract, 1 teaspoon cinnamon, nutmeg, and salt until the custard is smooth.
Pour the custard mixture evenly over the bread cubes, using a spatula to lightly press the bread down so it is fully submerged in the liquid.
Cover the dish with plastic wrap and refrigerate for at least 30 minutes, though for the best texture, an overnight soak is recommended.
When ready to bake, preheat your oven to 325°F (163°C).
In a small bowl, combine the remaining 2 tablespoons sugar and 1/2 teaspoon cinnamon; sprinkle this mixture evenly over the top of the bread.
Bake for 35 to 40 minutes, or until the custard has set and the tops of the bread are golden brown and slightly crisp to the touch.
Remove from the oven and let rest for 5 minutes before serving to allow the custard to firm up slightly.