• Heat the oven to 350°F. Grease an 8x8-inch glass or ceramic baking dish or metal baking pan with butter or baking spray.
• Spread out the croissant pieces on a rimmed baking sheet in a single layer. Toast them in the oven until they’re crisp and just beginning to brown, 8 to 10 minutes. Transfer the croissants to the prepared dish or pan. (The bread pudding will look prettier if you arrange the pieces so the cut sides face down and the flaky exterior sides are on top.)
• In a large bowl, whisk together the eggs, yolks, milk, cream, sugar, vanilla, cinnamon, and salt. Pour the mixture over the croissants, making sure to coat each piece. Some of the croissants may begin to float in the egg mixture—gently press on them to saturate them; they will settle as they absorb the liquid. Cover the dish with foil and refrigerate for 30 minutes.
• If you’re using a glass or ceramic baking dish, turn down the heat on the oven to 325°F. Keep the heat at 350°F for metal baking pans.
• Bake, covered, for 35 minutes. Remove the foil and scatter the hazelnuts over the top. Continue baking, uncovered, until the pudding is puffed, the bread and hazelnuts are toasted on top and a toothpick inserted in the center comes out clean, 30 to 40 minutes more.
• While the pudding is baking, prepare the sauce. Melt the butter in a heavy-bottomed medium saucepan over medium heat. Add in the brown sugar, cream, and corn syrup and stir constantly until the mixture comes to a boil. Continue boiling, stirring occasionally, until the syrup is slightly thickened, 5 to 7 minutes. Remove from the heat and whisk in the vanilla, espresso powder and salt. The syrup may seem bit clumpy and separated at this point—don’t worry. Set it aside to cool for about 20 minutes and it will thicken further. Whisk it again and it should now come together.
• Serve the bread pudding warm or at room temperature, with the espresso
• butterscotch sauce spooned over the top.

Make it a decaf

• If you’re going to serve this to kids and you’d rather not have them wired on caffeine, just omit the espresso powder. The homemade butterscotch sauce on its own is still something special.