Line a 3-quart baking dish with parchment paper and spray it with cooking spray.
In a large bowl, whisk together the eggnog and eggs to make the eggnog custard.
Slice or cube the croissants using a serrated knife. Toss the croissants with the eggnog mixture to coat everything evenly.
Transfer the bread pudding mixture to the prepared baking dish. Pour any extra eggnog custard over the top of the croissant pieces. Cover with plastic wrap and chill in the refrigerator for at least one hour or overnight.
When you are ready to bake the bread pudding, remove the baking dish from the refrigerator, take off the plastic wrap, and start to preheat the oven to 375°F.
Combine the melted butter, flour, brown sugar, nutmeg, and cinnamon in a medium bowl and stir until well mixed.
Sprinkle the crumble topping over the bread pudding evenly.
Bake the eggnog bread pudding for 35-45 minutes, until golden brown and the internal temperature is at least 160°F.
Remove it from the oven and allow it to rest 5 minutes before serving.
Nutrition facts are sometimes provided below and are calculated using an online calculator. With specific brands of ingredients and additions, omissions, or substitutions the nutrition facts may change. We encourage you to use your own nutrition facts calculator to obtain the most accurate nutrition facts for your meal.