Preheat oven to 200 degrees. Set a metal rack on a rimmed baking sheet. Slice Challah into 3/4-inch slices (about 12 slices). In a shallow dish or pie plate, whisk together eggs, half and half, sugar, vanilla, cinnamon, and nutmeg.
In a large skillet over medium-high heat, melt 1 tablespoon butter until foaming, swirling to coat pan. Working with 3 to 4 slices of bread at a time, dredge in egg mixture. Carefully tap against the side of the dish to remove excess, then set in pan.
Cook until edges are set and the first side is golden brown, about 1 to 2 minutes. Flip each piece and continue to cook until the second side is golden brown, about 1 to 2 minutes longer.
Transfer to oven to keep warm and repeat with remaining bread slices and batter (add more butter to the pan between batches). Dust generously with powdered sugar. Serve with butter and lime wedges or maple syrup as desired.
Challah: You can make it yourself or use store-bought. Either way, let it dry out for 3 to 4 days. You can also substitute Texas toast or any other thick-sliced bread.
Lime wedges: The squeeze of fresh lime juice instead of syrup is a little trick I learned from legendary food stylist Delores Custer. It's surprisingly tasty!
Yield: This recipe makes 6 servings, 2 slices each.
Storage: Store leftovers covered in the refrigerator for up to 3 days.
Croissant French toast: If you have leftover croissants instead of Challah, you can turn those into French toast, too.