I use brioche or challah for this French toast strata. Both breads are enriched, which means they are made with a lot of eggs and butter. The texture holds up so well to a rich custard. You can use other bread if you like, but the brioche and challah add the best flavor. Find it at your bakery or grocery store if you can. The loaves may come in different shapes, like braids or loaves, but either is fine. You can even slice brioche rolls into slices if that's all you can find.