Preheat oven to 350°F. Grease an 8×8 baking dish.
Add keto bread cubes to the dish.
In a mixing bowl, whisk eggnog, eggs, sweetener, melted butter, vanilla, cinnamon, nutmeg, and salt.
Pour the custard mixture evenly over the bread cubes.
Press gently to help the bread absorb the custard.
Let sit 10 minutes or refrigerate overnight.
Bake 30–35 minutes until golden and set.
Dust with powdered sweetener and serve warm.