Phase 1: Prepare the Night Before (Crucial for Best Results)

1. Prepare the Baking Dish: Generously grease a 9×13 inch baking dish with butter.
2. Layer the Bread: Arrange half of the bread cubes in an even layer in the prepared baking dish.
3. Distribute Cream Cheese & Blueberries: Scatter the cubed cream cheese pieces evenly over the bread layer. Then, sprinkle 1 cup of the blueberries over the cream cheese.
4. Add Remaining Bread: Top with the remaining bread cubes, distributing them evenly. Sprinkle the remaining 1 cup of blueberries over this top layer of bread.
5. Make the Custard: In a large bowl, whisk together the large eggs. Once lightly beaten, add the whole milk, heavy cream (if using), granulated sugar, vanilla extract, ground cinnamon, ground nutmeg (if using), and salt. Whisk thoroughly until the sugar is dissolved and all ingredients are well combined.
6. Pour Custard Over Bread: Slowly and evenly pour the egg custard mixture over the bread layers in the baking dish. Gently press down on the bread with a spatula or the back of a spoon to help it absorb the custard. Ensure all pieces are moistened.
7. Chill Overnight: Cover the baking dish tightly with plastic wrap or aluminum foil. Refrigerate for at least 4 hours, but preferably overnight (8-12 hours). This allows the bread to soak up all the delicious custard.

Phase 2: Bake on the Day of Serving

1. Preheat Oven & Prepare Dish: About 30-40 minutes before you plan to bake, remove the baking dish from the refrigerator and let it sit at room temperature. This helps it bake more evenly. Preheat your oven to 375°F (190°C).
2. Prepare the Streusel Topping (If Using):

   • In a medium bowl, combine the all-purpose flour, packed brown sugar, and ground cinnamon.
   • Cut in the cold butter using a pastry blender, your fingertips, or a fork until the mixture resembles coarse crumbs.
   • If using, stir in the chopped pecans or walnuts.

3. Add Topping & Bake: Uncover the baking dish. If you made the streusel topping, sprinkle it evenly over the top of the French toast.
4. Bake: Place the baking dish in the preheated oven. Bake for 45-55 minutes.

   • If you prefer a softer top, you can bake it covered with foil for the first 20-25 minutes, then uncover for the remaining time.
   • The French toast is done when the top is golden brown and crispy, the center is set (a knife inserted near the center should come out mostly clean, or with moist crumbs but no wet egg), and the internal temperature reaches 165-170°F (74-77°C). The edges should be bubbly.

5. Rest Before Serving: Once baked, remove the French toast from the oven and let it rest for at least 10-15 minutes before slicing and serving. This allows the custard to fully set and makes it easier to serve.