Can I assemble this the night before?
Yes, and you should. Cover tightly and refrigerate 8 to 12 hours. You can also prep it up to 24 hours ahead, but the bread will soften a little more the longer it sits (still delicious, just more custardy).
What bread works best?
Sturdy bread like brioche, challah, or Texas toast is perfect. Slightly stale bread is even better because it soaks up custard without turning to mush. If your bread is very fresh, cube it and let it sit out for 30 to 60 minutes, or toast it lightly in the oven to dry it out a bit.
How do I know it is done?
The center should be set (no liquid custard) and a knife inserted in the middle should come out mostly clean. A little moisture is fine, but it should not be wet. If you like numbers, the center should read about 160°F on an instant-read thermometer.
Can I make it less sweet?
Absolutely. Reduce the brown sugar in the swirl and skip the powdered sugar dusting. You can also serve the drizzle on the side so everyone chooses their own level of “holiday.”
Can I add meat or fruit?
Yes. Add cooked crumbled sausage or chopped cooked bacon for salty contrast, or tuck in berries and chopped apples for a fruitier vibe.
Do I really need to let it sit out before baking?
It helps it bake evenly, especially if you are using a glass baking dish straight from the fridge. Let it sit out 10 to 15 minutes while the oven preheats, but do not leave it out longer than about 30 minutes since it is an egg and dairy custard.