Step 1: Prepare the caramel apple layer. In a large skillet, melt 1/2 cup (1 stick) unsalted butter over medium heat. Once melted, add 1/2 cup packed light brown sugar, 1/4 teaspoon ground cinnamon, and a pinch of salt. Stir until the sugar dissolves and the mixture is smooth and bubbly, about 2-3 minutes.
Step 2: Add the sliced apples to the skillet. Toss gently to coat them in the caramel sauce. Cook for 5-7 minutes, stirring occasionally, until the apples are slightly softened but still hold their shape. Remove from heat and pour the caramelized apples evenly into the bottom of a greased 9×13 inch baking dish.
Step 3: Prepare the bread. Cut the bread into 1-inch cubes. Arrange the bread cubes in a single layer over the caramelized apples in the baking dish. Don’t press them down too firmly.
Step 4: Whisk together the custard. In a large bowl, whisk together 8 large eggs, 2 cups whole milk, 1/2 cup heavy cream, 1/4 cup granulated sugar, 2 tablespoons pure vanilla extract, 1 teaspoon ground cinnamon, 1/2 teaspoon ground nutmeg, and a pinch of salt until well combined and frothy.
Step 5: Pour the egg mixture evenly over the bread cubes in the baking dish, ensuring all the bread is thoroughly soaked. Gently press down on the bread to help it absorb the custard. Cover the dish tightly with plastic wrap or aluminum foil.
Step 6: Refrigerate the French toast bake for at least 4 hours, or preferably overnight. This allows the bread to fully absorb the custard, resulting in a more tender and flavorful bake.
Step 7: When ready to bake, preheat your oven to 375°F (190°C). Remove the dish from the refrigerator and let it sit at room temperature for about 20-30 minutes while the oven preheats.
Step 8: Uncover the baking dish and bake for 45-55 minutes, or until the top is golden brown, puffed, and the center is set. A knife inserted into the center should come out clean. If the top starts to brown too quickly, loosely cover it with foil.
Step 9: (Optional Streusel) While the French toast bake is baking, prepare the streusel topping. In a small bowl, combine 1/4 cup all-purpose flour, 1/4 cup packed light brown sugar, 1/4 teaspoon ground cinnamon, and 2 tablespoons cold unsalted butter, cut into small pieces. Use your fingertips or a pastry blender to mix until crumbly.
Step 10: Once the French toast bake is nearly done (about 10 minutes before it’s fully cooked), sprinkle the streusel topping evenly over the top. Return to the oven and continue baking until the streusel is golden brown and crispy.
Step 11: Remove from the oven and let it cool for 10-15 minutes before serving. This allows the bake to set up properly. Serve warm with a dusting of powdered sugar, a drizzle of maple syrup, or a dollop of whipped cream.