1. In a small saucepan over medium heat, melt the butter, brown sugar, and corn syrup together until smooth and bubbling, about 5 minutes. Pour this caramel mixture into a greased 9×13-inch baking dish.
2. Arrange the slices of French bread over the caramel in a single layer, slightly overlapping if necessary.
3. In a large bowl, whisk together the eggs, half-and-half, vanilla extract, salt, and cinnamon until well combined.
4. Pour the egg mixture over the bread slices, ensuring each piece is thoroughly soaked. Cover the dish with plastic wrap and refrigerate overnight.
5. The next morning, preheat your oven to 350°F. Remove the French toast from the refrigerator and let it stand at room temperature for about 20 minutes.
6. Bake the French toast uncovered for 35 to 40 minutes, or until the edges are golden brown and the center is set. Allow it to cool slightly before serving.
7. Dust with powdered sugar before serving, if desired, and enjoy the delightful caramelized crust and creamy interior.

Tip from my kitchen: To achieve a perfectly caramelized top, I sometimes use a culinary torch after baking to gently crisp the sugar on top, reminiscent of a true crème brûlée.