Preheat oven to 475°. Place water on range top to boil for a water bath.
With a serrated knife, remove the side crusts from the bread. Cut into ¾-1 inch dice. You should have 5 cups. Reserve the cubed bread in a large mixing bowl.

For the eggnog custard, in another bowl thoroughly whisk together the eggs, yolks, sugar, half and half, rum, vanilla extract, and nutmeg. Pour over the bread cubes.

Spray a 12-cup muffin tin with vegetable cooking spray. Ladle the bread/eggnog mixture gently and evenly into the muffin tins. (The big cubes sticking up to look nice.) Place the filled muffin tin in a roasting pan. Transfer to the preheated oven and carefully pour the hot water creating a water bath for the muffin tin to sit in. Bake 15 to 20 minutes until the tops are nicely browned, and a toothpick inserted into the center comes out clean. Bread pudding may be served warm or cold. And vanilla ice cream or whipped cream, if using.