Prepare the baking dish: Preheat your oven to 350°F (175°C) for later, but first, generously grease a 9x13-inch baking dish with 2 tablespoons of softened butter. This prevents sticking and adds flavor.

Cube the bread: Cut the challah into 1-inch cubes. Spread them evenly in the prepared baking dish. If your bread is fresh, toast the cubes lightly in the oven at 350°F for 5 minutes to dry them out – this helps absorb the custard better.

Make the custard mixture: In a large bowl, whisk together the eggs, half-and-half, whole milk, granulated sugar, vanilla extract, orange zest, and kosher salt until smooth and well combined. Bullet points for clarity:

Ensure eggs are fully incorporated to avoid lumps.

Taste the mixture – it should be sweetly custardy with a citrus hint.

For extra fluffiness, let it sit for 2 minutes before pouring.

Soak the bread: Pour the custard mixture evenly over the bread cubes. Gently press down with a spatula to ensure all pieces are submerged. Cover the dish tightly with plastic wrap or foil and refrigerate overnight (at least 8 hours). This is the magic step that makes this homemade Barefoot Contessa Baked French Toast Casserole recipe so tender and flavorful!

Prepare the streusel topping: In a medium bowl, combine the brown sugar, flour, cinnamon, and chopped pecans (if using). Cut in the cold butter cubes using a pastry cutter or your fingers until the mixture resembles coarse crumbs. Bullet points for best results:

Keep butter cold to create that crunchy texture.

Don't overmix – lumps are good for the streusel.

Store covered in the fridge if prepping ahead.

Assemble and bake: Remove the casserole from the fridge 30 minutes before baking to come to room temperature. Preheat oven to 350°F. Sprinkle the streusel evenly over the top. Bake uncovered for 40-45 minutes, or until the top is golden brown and the custard is set (it should jiggle slightly in the center). If the top browns too quickly, tent with foil.

Rest and serve: Let the casserole cool for 10 minutes before serving. This allows the flavors to settle and makes slicing easier.