📖 Instructions

1. **Prepare Your Bread (The Night Before is Best!):** First things first, get your bread ready. You'll want about 1 pound of challah, brioche, or even a good quality day-old French bread. The key is to use slightly stale bread; it soaks up the custard much better without becoming soggy. Cut the bread into 1-inch cubes. Don't worry about perfect uniformity, a little rustic charm is good! Spread these cubes out on a large baking sheet and let them sit uncovered on your counter for a few hours, or even overnight, to dry out a bit. This step is crucial for that 'bakery-style' texture.
2. **Grease the Dish & Arrange Bread:** Lightly grease a 9x13-inch baking dish with butter or non-stick cooking spray. I like to use a little butter for extra flavor, but use what you have! Evenly distribute half of your bread cubes in the bottom of the prepared dish. Scatter 1 cup of fresh or frozen blueberries (no need to thaw if frozen) over this first layer of bread. Then, add the remaining bread cubes on top.
3. **Whisk the Custard Together:** In a large mixing bowl, whisk together 8 large eggs until they're well combined. Pour in 2 cups of whole milk (or half-and-half for an even richer casserole!), 1/2 cup granulated sugar, 2 teaspoons of pure vanilla extract, and a pinch of salt. Whisk vigorously until everything is thoroughly mixed and the sugar has dissolved. You want a smooth, uniform custard mixture.
4. **Pour and Soak:** Carefully pour the egg custard mixture evenly over the bread cubes in the baking dish. Gently press down on the bread with the back of a spoon or spatula to ensure all the bread pieces are submerged and have a chance to soak up that delicious liquid. This is how we get that custardy interior, so don't skimp on the soaking!
5. **Refrigerate (Crucial for Flavor & Texture):** Cover the baking dish tightly with plastic wrap. Place it in the refrigerator for at least 4 hours, or ideally, overnight. This long soak allows the bread to fully absorb the custard, resulting in a perfectly tender and flavorful French toast. If you skip this, your casserole might be dry in some spots, so please don't!
6. **Make the Streusel Topping:** While the casserole is soaking or just before you're ready to bake, prepare your streusel. In a medium bowl, combine 1/2 cup all-purpose flour, 1/4 cup granulated sugar, 1/4 cup packed light brown sugar, and 1/2 teaspoon ground cinnamon. Use a fork or your fingers to mix these dry ingredients. Add 1/4 cup (4 tablespoons) cold unsalted butter, cut into small pieces. Work the butter into the flour mixture with your fingertips or a pastry blender until coarse crumbs form. Don't overmix; you still want some buttery bits. Pop it in the fridge until you're ready to bake.
7. **Preheat Oven & Get Ready to Bake:** When you're ready to bake, preheat your oven to 375°F (190°C). Take the casserole out of the refrigerator about 20-30 minutes before baking to let it come closer to room temperature. This helps it bake more evenly.
8. **Add Streusel and Bake:** Uncover the casserole dish. Evenly sprinkle the prepared streusel topping over the top of the soaked bread. If you want, scatter an additional 1/2 cup of fresh blueberries over the streusel for an extra burst of fruit. Place the baking dish on a large baking sheet (just in case of any bubbling over) and bake for 45-55 minutes, or until the top is golden brown, the streusel is crisp, and the center is set. A knife inserted into the center should come out mostly clean. If the top starts to brown too quickly, you can loosely tent it with aluminum foil.
9. **Cool Slightly and Serve:** Once baked, remove the casserole from the oven and let it cool for about 10-15 minutes before serving. This allows the custard to set a little more, making it easier to serve. Serve warm with a dusting of powdered sugar, a drizzle of maple syrup, and maybe a dollop of whipped cream. Trust me, it's heavenly!