Grease your casserole dish with extra butter or oil.
Cut challah bread into larger 2” cubes.
Place the bread cubes into the greased casserole dish.
In a large bowl, whisk together the remaining ingredients besides the powdered sugar.
Pour mixture over the top of the bread evenly and let soak through.
Cover with plastic wrap and refrigerate for at least 6 hours or up to 48 hours.
When you’re ready to bake, preheat the oven to 350 F. Remove plastic and bake for 50-60 minutes. Every oven is different so make sure to watch to prevent burning. Remove when the egg mixture looks set and parts of the bread are crisp.