Step 1 - Prepare the Oven and Baking Dish: Preheat your oven to 350°F (175°C). Lightly butter an 8 × 8-inch casserole dish, making sure to coat the bottom and sides so the bread pudding does not stick. Set the dish aside while you prepare the bread.
Step 2 - Cut and Prepare the Bread: Cut the bread into roughly 2-inch cubes until you have about 6 cups. Brioche or challah will give your bread pudding a rich, buttery texture, but you can also use sourdough or another type of bread you have on hand. Slightly stale bread works especially well because it absorbs the custard without falling apart too quickly. If your bread is fresh, spread the cubes on a baking sheet and let them sit out to dry, or place them in a 250°F oven for about 10 minutes. Allow the bread to cool before using it.
Step 3 - Arrange the Bread in the Dish: Transfer the bread cubes to the buttered casserole dish. Spread them into an even layer, arranging some of the crusts facing upward for a more attractive finish. If you want to add toasted pecans, chocolate chips, dried fruit, or toasted coconut, scatter them among the bread cubes now.
Step 4 - Warm the Cinnamon Custard Mixture: Add the whole milk, granulated sugar, butter, salt, and cinnamon to a saucepan. Place the saucepan over medium heat and stir occasionally until the butter has melted and the milk is warm. Do not bring the mixture to a boil. Once the butter has melted and the ingredients are well combined, remove the saucepan from the heat.
Step 5 - Cool the Milk Mixture: Let the warm milk mixture cool for about 10 minutes. This is important because adding eggs to very hot milk can cause them to scramble, leaving unwanted cooked egg pieces in your custard.
Step 6 - Add the Eggs and Vanilla: Crack the eggs into a small bowl and check for any pieces of shell. Whisk the eggs into the cooled milk mixture one at a time until each egg is fully incorporated. Add the vanilla extract and whisk again until the custard is smooth and evenly mixed.
Step 7 - Pour the Custard Over the Bread: Slowly pour the prepared custard over the bread cubes in the casserole dish. Move the bread around gently if needed so the liquid reaches the bottom and coats all the pieces. Check that there are no dry bread cubes remaining on top. The bread should be evenly soaked in the custard.
Step 8 - Let the Bread Soak: Leave the assembled bread pudding at room temperature for about 20 minutes. This gives the custard time to penetrate the bread, helping the finished pudding turn soft and moist throughout. If you want to prepare it ahead, cover the dish and refrigerate it until you are ready to bake.
Step 9 - Bake the Bread Pudding: Place the casserole dish in the preheated oven and bake at 350°F (175°C) for 40–45 minutes. The top should become nicely golden, and a knife inserted into the center should come out clean. If the center still looks wet or loose, continue baking for a few more minutes and check again. Once baked, remove the dish from the oven and let the bread pudding rest briefly while you finish the sauce.
Step 10 - Combine the Sauce Ingredients: To make the vanilla pouring custard, add the whole milk, heavy cream, butter, and packed light brown sugar to a medium saucepan. Place the saucepan over medium heat and stir occasionally with a whisk as the butter melts and the sugar dissolves. You can substitute 2 cups of half-and-half for the milk and cream if preferred.
Step 11 - Prepare the Cornstarch Slurry: In a small bowl, combine the cornstarch with ¼ cup of water, bourbon, dark rum, or brandy. Whisk until the cornstarch has completely dissolved and the mixture is smooth. This slurry will help thicken the sauce and give it a rich, pourable texture. If you use alcohol, remember that some alcohol may remain after cooking.
Step 12 - Thicken the Vanilla Custard Sauce: Once the milk and cream mixture begins steaming and the butter has melted, slowly pour in the cornstarch slurry while whisking constantly. Continue stirring over medium heat until the sauce thickens noticeably. This should happen fairly quickly. If the mixture begins to thicken too fast, lower the heat to prevent it from sticking to the bottom of the saucepan.
Step 13 - Add the Vanilla and Finish the Sauce: Remove the thickened sauce from the heat. Stir in the vanilla extract or vanilla bean paste until fully combined. Add a pinch of salt if you want a little extra contrast against the sweetness. The finished sauce should be smooth, creamy, and thick enough to coat the back of a spoon while still being easy to pour.
Step 14 - Serve the Bread Pudding: Spoon the warm vanilla custard sauce over the freshly baked bread pudding. Cut the pudding into portions and serve while warm, adding more sauce to each serving if desired. You can also serve it with a scoop of vanilla ice cream for a richer dessert.