1/2-large (2-pound) loaf challah bread, torn into 1½–2-inch pieces (about 8 cups)
1 3-inch cinnamon stick
1/2 vanilla bean, split lengthwise
1 1/2 cups heavy cream
1 1/2 cups whole milk
1/3 cup granulated sugar
1/4 teaspoon kosher salt
1 3-inch strip orange zest
1/4 cup (1/2 stick) unsalted butter, melted, divided, plus more for pan
1 large egg
2 large egg yolks
2 tablespoons raw sugar
1/4 cup sliced almonds (optional)
Preheat oven to 300°. Spread torn bread on a rimmed baking sheet and bake, tossing halfway through and reducing oven temperature if bread is getting too golden, until pieces are very dry and slightly toasted, 25–35 minutes. (Dry bread will absorb the custard without disintegrating, which is why this step is important.) Let cool, then transfer to a large bowl.
Meanwhile, heat cinnamon, vanilla bean, cream, milk, granulated sugar, and salt in a medium saucepan over medium-high. As soon as mixture starts to boil (watch closely or milk will boil over top of pot!), remove from heat. Whisk in orange zest and 2 Tbsp. butter and let steep 30 minutes. Pluck out and discard cinnamon stick, vanilla bean, and orange zest.
Brush a 1½–2-qt. baking dish with butter. Pour milk mixture into a blender. Add egg and egg yolks and blend, starting on low and increasing speed to high, until mixture is light and foamy, 20–30 seconds. Pour over reserved bread and toss to coat. Scrape into prepared pan. Cover tightly with plastic wrap and chill at least 3 hours and up to 12; this gives bread time to evenly soak up custard.
Arrange a rack in center of oven; preheat to 300°. Brush remaining 2 Tbsp. butter over cold bread pieces. Sprinkle with raw sugar, then top with almonds, if using. Bake bread pudding until lightly golden, puffed, pulling away from edges of pan, and butter is bubbling, 30–40 minutes. Let cool 1 hour before serving.
Do Ahead: Bread pudding can be made 1 day ahead. Let cool; cover and chill.
For Chocolate Bread Pudding
Add 6 oz. chopped bittersweet chocolate (70% cacao or higher) and 2 Tbsp. unsweetened cocoa powder to scalded milk mixture instead of butter and whisk until melted and smooth.
When ready to bake, top bread pudding with 1 oz. chopped bittersweet chocolate. Sprinkle with raw sugar, then top with ¼ cup chopped pecans instead of almonds. Bake as directed.
For Coconut Bread Pudding
Add one 13.5-ounce can unsweetened coconut milk instead of heavy cream to whole milk mixture. As soon as mixture bubbles, remove from heat and whisk in 2 Tbsp. virgin coconut oil instead of butter and a strip of lime zest instead of orange. Let steep 30 minutes. Pluck out and discard cinnamon stick, vanilla bean, and lime zest.
Brush baking dish with 2 Tbsp. melted virgin coconut oil instead of butter. Brush 2 Tbsp. melted virgin coconut oil instead of butter over cold bread pieces. Sprinkle with raw sugar, then top with 1/4 cup unsweetened coconut flakes instead of almonds. Bake as directed.
From Bon Appetit