Step 1: Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish with butter or non-stick spray.
Step 2: Place the cubed gluten-free bread into the prepared baking dish. If your bread is fresh, you can toast the cubes lightly in the oven for 10-15 minutes to dry them out slightly before adding them to the dish.
Step 3: In a large bowl, whisk the eggs until they are light and frothy.
Step 4: Add the granulated sugar, milk, melted butter, vanilla extract, cinnamon, nutmeg, and salt to the egg mixture. Whisk everything together until well combined and the sugar has largely dissolved.
Step 5: Pour the custard mixture evenly over the bread cubes in the baking dish. Gently press down on the bread with a spoon or spatula to ensure all the cubes are submerged and soak up the liquid. Let it sit for at least 30 minutes, or up to an hour, in the refrigerator to allow the bread to fully absorb the custard.
Step 6: If using optional add-ins like raisins, chocolate chips, or nuts, sprinkle them over the top or gently fold them into the bread mixture before baking.
Step 7: Bake for 45-60 minutes, or until the top is golden brown and a knife inserted into the center comes out mostly clean. The center should still have a slight jiggle. Let the gluten free bread pudding cool slightly before serving warm with your favorite toppings.